Lean of Peak (LOP) Engine Operation Explained
Lean of Peak (LOP) - it's the holy grail of engine operation for some, and pure evil for others. You are not sure who is right? This video shows what really happens when we fly lean of peak, how it is different from rich of peak (ROP), and how at different times either LOP or ROP can be the right choice.
Join me on a flight where we collect and compare data from running the engine first ROP and then LOP. We'll explore how rich or lean mixtures influence exhaust gas temperature (EGT) and cylinder head temperature (CHT), and of course fuel economy (and thus the range of your airplane). We'll also discuss the "red box", which is an area in which the engine should not be operated in, and why it is difficult or even impossible for some engines to run lean of peak well.
While great care has been taken to ensure the information presented in this video is accurate, different airplanes and different engines may require some practical adaptation to get the most benefit out of LOP and to prevent harm to the engine. Therefore, rely on this video for the background, but team up with a flight instructor familiar with lean of peak operations in your type of airplane and with your type of engine to apply what you learn here.
A couple of URLs from this video:
John Deakin's "Pelican's Perch" article index:
www.avweb.com/news/pelican/18...
Advanced Pilot Seminars:
www.advancedpilot.com
Support Martin's work on Patreon:
/ martinpauly
Martin, as a military and professional airline pilot with over 27,000 hours, as well as Bonanza owner of fifteen years, I have to say I am impressed again with your ability to explain often confusing topics in simple terms. Nicely done and keep up the fine work!
Thanks, Bruce - I appreciate the kind feedback. There are a lot of misunderstandings and myths about mixture management when in reality it is not such a difficult topic. - Martin
Martin, as a retired NASA astronaut, space shuttle captain, and SR-71 owner for 20 years, I have to say I'm impressed with your ability to explain how to lean a piston engine in only half an hour. Good job and THANK YOU for making such quality content!
I appreciate the kind words. I do have one question for you: how does one become an SR-71 owner? (Other than being a tax payer) Best regards, Martin
Hmmm...SR-71 "owner". NOT! Also, space shuttle "captain". NOT! Anyone familiar with Shuttle crew knows that the term is Commander...never Captain.
😆
woosh
@martinpauly I think this was said in humour....because of all the other people replying and quoting their resumes. Like any of that has anything to do your video....
Martin, as both an aerospace engineer and a retired USAF Navigator (responsible for both preflight fuel calculations as well as enroute fuel management), I wholeheartedly endorse your video! You not only nailed the issues solid, but you covered the exceptions in a clear and notable manner. EXCEPTIONALLY well-done!
Thank you very much for the encouraging feedback, Justin. Much appreciated.
cok
I could not agree more...but I am far from a aerospace engineer! haha Great video Martin!
In my days, the copilot did all the fuel calculations and managed the inflight fuel management, not the Nav.
Had Martin been my professor for thermodynamics I probably would have stayed in engineering 20 years ago. Thermodynamics is hard enough without it being explained in a broken chinese accent!
Absolutely on of the best videos summing up engine management! Great work!
Hey Martin, GREAT video. Probably the best video I have ever seen on the topic. I am going to bring up the topic in a video and refer my viewers to this video for a better explanation.
Thank you, Baron Pilot - much appreciated!
And Martin, I just watched the video since Baron Pilot suggested it, and it reinforces all I thought I knew about LOP operations, and added additional information. Very well done, very easy to understand, and very informative.
Thank you for the feedback, Gary. I am glad you found it useful.
I loved the bloopers at the end, thx for including those
Glad you enjoyed those bloopers! - Martin
I knew a large portion of that, but the bits I learned are extremely helpful! Thank you for the very detailed explanation.
Wow! Despite having many people, including my mechanic trying to explain me Lean of peak, I never got to fully understand. But thanks to your video, now I can feel safe using lean of peak
It's really not that difficult a topic, is it? Probably feels scarier than it is to most pilots. - Martin
The best video on Mixture Leaning I've ever seen. Thanks a lot !!!
Merci beaucoup! - Martin
You have a very special gift as a teacher! Even pointing to our left and right vs yours! This is a fantastic video, I will watch it multiple times. Thank you for your effort and devotion for our benefit, thank you thank you!
! ! ! SIMPLY AWESOME EXPLANATION ! ! ! Thank You Very Much !
You are a fantastic teacher! Pretty good video editor too. First rate educational material.
Thank you, John! It's been fun making and editing this video.
Despite reading several articles on the subject, I never really understood the mechanics behind the decision process. Very good explanation that shows a superior depth of understanding - BRAVO!
Thank you very much, Dave. I'm glad you found it helpful.
Excellent job as usual Martin. I finally have a much clearer understanding of this subject.
EXCELLENT VIDEO, Martin. You’ve completely demystified engine power and thermal management for me. Thank you.
One of the most informational videos I have ever seen on KZhead! Great job! Outtakes were classic.
Thank you, Robert - I'm happy to hear you found it useful. - Martin
Great video! Thank you for putting this out there
Thanks for the feedback, TFP. Glad to hear you liked the video.
Unbelievable video. I fly a 1980 A36 (520) and have really been perplexed by running lean of peak the last couple years. Thank you for this! Exactly what was needed!
Dude's getting the same fuel economy as my pickup truck when pulling a trailer. That's extremely impressive, especially for a Bonanza.
At three times the speed!
Martin, thank you so much for this video. I have tried to understand LOP from several sources, leaving a lot of questions behind. You explained it so simple and now I finally know what´s going on and how to deal with the airplanes I am flying. Also I love the way you explain and show examples on the instruments and charts. Thank you !!
You are very welcome - glad to hear it was helpful. - Martin
This is a terrific video Martin. I wish more people would make videos as comprehensive as you have. This is a true reference resource. I know how much work it is to make this happen, so many thanks to you! And, by the way, thanks for recently accepting my invitation on LinkedIn. All the best, Josh
Thank you for the kind words, Josh. Regards, Martin
Best video I’ve seen on LOP. Thanks Martin.
EXCELLENT video - VERY high production standards and an excellent, well written script JR
Excellent discussion and teacher. I am reminded of my automotive racing days with normally aspirated carbureted engines. I loved the challenge of setting up an engine with various fuel flows, jets, and cam angles for the best performance of the day. This was all before fuel injection. It was fun and I learned a lot. I had to set up my own gauges inside the car for manifold pressures, EGT, and CHT. The science was fascinating! Thanks, Martin!
Thank you for the kind words, Rich. Yes, engines are fascinating, aren't they? - Martin
Hi Martin, this was by far the best from all other videos I have watched regarding the topic. Thank you.
Thank you, Abraham. Glad you liked it.
Ok Martin, you are getting better and better with every video
Fantastic video! I attended the first Advanced Pilot Seminar in Ada. I ran the aircraft side of an engine shop at the time and we broke in engines at high power settings but LOP. It absolutely works well in many situations if managed properly. Many tuned induction engines don't need special injectors but if they do, GAMI is there to help. They do great things for aircraft there.
Great video explanation, Martin. I'm an instructor in a flying club and will be sharing this as required reading.
Thanks - glad to hear you think the video is helpful!
Absolutely the BEST video on running LOP!!! Congratulations Martin... und ja...vielen Dank !
Thank you very much! - Martin
Martin, I came across your tail wheel training with Doug Rozendaal as I was refreshing that skill. That was great. Then looking further I found your explanation of Lean of Peak operations here. You gave such clear instruction that you have expanded my understanding of the chatter I hear from my EAA friends that have CHT and EGT monitoring in their cockpits. This is new from my general aviation experience. Thanks
this is the best tutorial of the JP EDM700! searched long, found many. But no realy good ones..yours is great.
Excellent video... By far the best video on this topic.
Thank you, Steven.
How do you have manage to do such a great job on these and still have a real job? All your videos are first class.
Thank you, David. Making videos is just a hobby, and very different from my day job. Maybe that's one reason I like it so much - a welcome change from the office chores.
Subscribed! Like many before me already commented, this is THE BEST video on the topic out there! Thank you, Martin for taking the time and trouble to thoroughly prepare and post this! Your content is very enjoyable for us GA enthusiasts to watch! Question: Have you considered preparing a video summarizing how you decided to purchase a Bonanza, the flight training you undertook getting comfortable flying the Bonanza before you purchased it, and the important factors you considered in your search to purchase an airplane and how you decided to go with the Bonanza (usage, size, comfort, range, cost etc.)? As an instrument-rated private pilot never purchased a airplane, I am curious about the thought process and analysis you went through and this seems like a great GA topic that would interest many of us. Would you do anything differently with the benefit of hindsight? Thanks so much!
Just what I needed!! Great informative video and put together very well, thanks!
Glad to hear, Chuck. Thanks!
Lot's of information presented very well in a short amount of time! Great job! I discovered flying lean of peak right after I bought my Mooney M20F in 2013 and also operate the engine lean of peak most of the time. Highly recommended!
Thanks, Bernd - or should I say "Danke"?
Whatever pleases you... - I'm current and Level 6 in both languages... ;-)
I almost quit watching at "Hello Bonanza Fans" It was hard to get past that part. I pressed on however. Outstanding Info. Subscribed.
Just Plane Silly Hey Bryan, I’m glad you were able to make it past the word “Bonanza” - I know, it’s hard to be a fan of an airplane in which pilots practice slow flight at the taxi speed of a Cirrus. :-) Thanks for chiming in; I love your videos!
HAHAHAHAHA!!!!!!! Thank you! I have already shared this video with a handful of people. Very well done and very well simplified. If you go to Osh this year, let me know. I will buy you a beer!
How could I turn down a beer - thank you! I don't know yet if I'll be in Oshkosh this year. If I go, it'll be at the end of the event, because it is the same week as RAGBRAI, a cycling event (which is really just an athletic euphemism for "weeklong party on bikes") here in Iowa - so I am torn, and RAGBRAI usually wins. At any rate, I do hope to run into you one of these days somewhere.
Just not in the air.
@@martinpauly I just hit the like button. Actually Bryan is a changed man 😂 He seems to be creating some sort of a promotional video for the Bonanza one of these days.
What a great lesson. Most folks can’t describe much less define how to lean an engine and why it matters. Your video makes it very clear why it matters.
Thank you for the kind words, Ed. - Martin
Very well done video! Kas Thomas, past editor of Light Plane Maintenance also explained all of this well, back in the ‘70s, in his book ‘Fly The Engine’. The book covers complete engine care, & has now been re-published.
Well done, Martin. I've been an advocate of LOP for many years, and your explanation is better than I could have done. My Cessna 421B has used LOP for the 40 years I've owned her, and the big GITSO 520s always make it well beyond TBO. PS: Loved the outtakes.
Thank you, Raymond. Regards, Martin
VERY good and informative, clear, and precise video Martin! Do more like this one...excellent! I like all your videos, very informative and good info, especially for us new pilots! I actually took the Advanced Pilot Seminar online and you just about covered it all! Since I have taken that course I have run LOP with most cruise operations. I have a Cessna 182Q with the 0-470U carbureted engine but with a belt driven Supercharger. This supercharger allows me to fly higher with more power and a nice side effect of the supercharger is being able to easily run LOP. Depending on altitude and throttle settings, my GAMI scores are around .3 to .6 and I can get to about 50 LOP. I am assuming the supercharger warms the air up like carb heat would which helps even out the fuel distribution. There is a nice and easy formula that you can use calculate your horsepower when LOP. It's based on your compression ratio. Most engines have an 8.5:1 compression so you use a factor of 14.9 (Turbo engines have a 7.5:1 compression ration which is a factor of 13.7). All you have to do is multiply 14.9 X GPH = Horsepower. In my case, I run around 10.6 to 10.9 GPH. So, 14.9 X 10.9 = 162 HP. 162/230(max HP) = 71% HP and this is all running 25 to 30 LOP! Keep in mind this formula does not work ROP. Another side effect of running cooler and leaner is less chance of plug foul, less carbon building up in the engine, and probably longer time between TBO!
Thank you, Roger. I think you may be right about the supercharger (and the warmer induction air it produces) helping with LOP - glad it works with your engine. And you are right, there are other benefits of flying LOP that I didn't cover in this video.
Martin, sorry by not noticing the altitude before sending out the question. I fly an RV-7A and Piper Arrow and this topic is very interesting and I would like to apply on my flying. Your videos is by far the most complete and easy to understand I’ve seen so far about this topic, congrats and thanks for uploading. Cheers from Brazil (Ps, Steven was somehow my phone typing correcting fault) lol !
Great out-takes, btw! They really illustrate how much work is put into these videos, and we thank you for that. Cheers.
Thank you, Spike. - Martin
Martin, still the best explanation on the subject. Thanks for all you are doing in educating us general aviation pilots. As a thank you, I'll send you some red paint for your mixture control. ☺ Best,
The red paint comment made me laugh! :-) Thanks, Dennis. - Martin
If EAA sees this video you will be doing a lecture at Air Venture!!! I have struggled understanding LOP and have been flying my BO 50 ROP. I have the same JPI monitor so it’s like you were in my plane showing. Fantastic job Martin. Have you programmed your LPI to lean find LOP? I know it’s an option. I’ll be going up with my CFI and playing with mine soon.
Thank you, Thomas. Please don't fly your Bo 50 deg ROP - now you know why not, at least not at high power settings. The JPI monitor has a "lean find" function, but I never use it. Once you know which cylinder to watch, it's easier to just go by EGT.
Only fly that way at cruise, full rich for climb. I noticed you leaned at 2500 RPM, is that where you fly?
Yes, for cruise and descend - that seems to be a happy place for my engine. For take-off and climb, I run at 2,700 RPM.
Was lucky to watch a similar presentation in Oshkosh this year (2021), Thanks Bonanza Society, and thanks Martin! Any updates on where one may want their CHT, when running lean of peak? (I thought you had said to stay under 400, but around 350? Is that accurate in a 1968 Bonanza… Thanks
Best LOP video session I've ever seen. Well done and thanks for taking the time to share this with us.
You are welcome, Richard, and thanks for the feedback.
Finally,.. Thanks for making this. I really needed someone to go thru it step by step like that.,, Great job !
You are welcome - glad you found it useful. If you happen to be at Sun 'n Fun next week, I'll give presentations on LOP both Friday and Saturday morning. - Martin
With electronic ignition you can take even more advantage of LOP. The LOP robs the engine of power since the combustion charge burns more slowly and the piston has already started "down" from top dead center by the time you have full burn of the combustion charge. With electronic ignition you can change the ignition timing, advance the spark, and return to full combustion closer to top dead center on the piston. This gives you more power out of the fuel you are burning and even more economy.
That's correct. It's a shame we don't see electronic ignition being used more widely in piston GA airplanes. Regards, Martin
@@martinpauly As electronics engineer I full agitate against unnecessary complication when goal may be achieved witch simpler solutions. Magnetos are highly reliable, cheap and easy to maintenance. Electronics improve efficiency but is more prone to malfunction. OK, as most of systems in aviation should be redundant as magneto is (two independent systems on cylinder). Next problem to solve is powering, magnetos works autonomously but electronic ignition depends on external electricity. More points to probable failure for electronic - from engine shaft sensor/actuator, by wiring, connections to spark module at end - less trustworthy system for pilot than simple magnetos, even with more fuel cost. Life is priceless.
How is the net result of leaning different than just reducing the manifold pressure or throttle?
You can achieve the same power reduction by either (A) leaning (pull the mixture back from ROP to LOP) or (B) reducing manifold pressure (pull the throttle back). Either way you are getting more efficient (in terms of gallons of fuel per nautical mile) than before the power reduction because the resulting airspeed is lower (i.e. lower drag). Doing (A) has additional fuel efficiency on top of (B) because the same power can be produced with less fuel flow LOP compared with ROP, plus (A) also results in a cooler engine (lower CHTs) - the two main benefits of running LOP. Regards, Martin
This is an incredible video. Most instructors will show the lean procedure but never explain what is happening or why you must have the mixture setting at a certain level. After years of flying, I now understand much more about leaning and will be able to lean from intelligently than mechanically. Thank you for sharing this information. Very well done.
Great Video, Martin! You nailed the LOP Mystery in a short Video!
Danke, Timo - das freut mich.
24:58 S.T.F.U. Made me laugh out loud!
Yup. Everybody likes outtakes. :-)
The best vid I have found on LOP/ROP operation so far! Excellent job!
Danke schön! :-)
Not only was this video produced in a very professional way, but the content was presented in a well organized way, communicated clearly and at a great pace to keep up with it. Nice transitions back and forth from the cockpit, hanger, and chart, when it made sense, without it being annoying or distracting. One of the best videos on ANY subject I have ever seen. And for the content, a fantastic way to explain Lean of Peak and show real numbers while doing so. And, not in a fanatical way, saying this is the only way to do it, but that there are times where it makes sense, and how to do it right. And the presentation of the Red Box was well done. I recently flew with a friend in a 172 and as we leveled out, I was looking for the CHT to see where we were. So I asked him how do you adjust your mixture? And he said using the tach. I would be scared to just use a tach to adjust the mixture as you don't know if you're damaging the engine putting it in the red box. That was how I always used to do it was just on the CHT that was given to me back in the 70's and 80's. Now with these Engine Monitors, there is no reason to not be more aware of CHT and EGTs and treat your engine better, while either getting better power, or more economy. Well done! Have you considered doing a video on constant speed props similar to this, showing the POH and what the numbers mean, how to apply them, the correct order doing transitions up and down, etc.
That was a great video, one of the best that I’ve seen on lean of peak operations. Thank you.
Thanks, Michael. Glad you found it useful. - Martin
You’re an incredible communicator. Great info. Thank you for the work you put into that.
Thanks, Randy. It's always fun making these videos, and a great learning opportunity for me - every time!
Excellent video, Martin. I learned several things from this. You did a great job of explaining this ... and in a simple & understandable way. Also, the graphics were great. Please, keep up the great work. Cheers, Chuck
Thank you :-)
This is an excellent, comprehensive explanation. Thank you!
Thank you, Mark. If you happen to be in Oshkosh this year, I will give a Lean-of-Peak live presentation there - come join if you’re around. Regards, Martin
Great video and I enjoyed the out takes! Keep doing these... you’re really good at it!
Thank you! :-) - Martin
Thank you. This is the best information I’ve ever seen on lean of peak. I will have to say,your outtakes are fantastic too, I enjoyed them.
Glad it was helpful! And yes, everybody loves outtakes 😁 - Martin
Clear and concisely explained. Thank you. I used to tune carbureted two stroke racing motors. Lean was bad due to the cooling factor of the fuel. Your 4 cycle tuning chart, backed up by actual demonstration makes all the sense in the world. The 1400F temperature still scares me with aluminum.
Martin is an exceptional teacher an Areo Guru award is in order.
That was a great video. Clear and detailed. Also, the outtakes were great!
Thank you, Mark. Glad to hear you liked the video. And yes, everybody seems to love the outtakes! :-)
Martin, this is an excellent video I have watched several tines. The pace and clarity of explaining things in a very structured way is unique. Thanks for this. It is very helpful.
Thank you - happy to hear this worked well for you. - Martin
Yet another fantastic video Martin. Well done!
Thank you, James! :-)
This is the best video for LOP how to. Great job!!
Thank you - glad to hear you find it helpful.
Absolulety loved the video!!! AWESOME WORK!!!! Please make more. I've learned a lot and now have a good understand of LOP & ROP. Thank You!
Thank you, Mario. Any suggestions for other topics you'd like to see covered with similar videos?
Thanks for sharing...... Im a pilot that flew a lot of turboprop and turbines ,and now I will start piston engines....... It is new for me and Im learning a lot from you.Congrats! 👍👍
This was awesome. I’m glad I stayed up for the chalkboard at the end.
Thanks, UAL1kFlyer.
Thank you for this video. It is clear that you took a great deal of time and effort to help others. Noble and appreciated.
Thank you for the kind feedback, Robert. Yes, this one took quite a long time to make. But it was a fun project! - Martin
I've been looking at this subject for several weeks now and have read most of John Deakins' articles on Pelican's Perch, but I have to say that his video was the most lucid and well laid-out distillation of this complicated subject that I've seen anywhere. Really excellent. Thank you very much.
Thank you for the kind words. - Martin
What a wonderfully well done video and explanation. Thank you for taking the time to produce it. Cheers!
My pleasure! - Martin
Great video! Thank you for taking the time to help educate us on this subject. LOP and ROH has been somewhat of a mystery to me and I will certainly try this when my EDM-930 is installed in the next couple of weeks on my J35 Bonanza with the IO-520.
Thanks. Your EDM-930 will show you everything you need to know to understand how your engine is running and whether it's happy - good choice! - Martin
Wow! Everything I always wondered about! Thank you! Excellent graphics and animations. It ain't easy! You did it!
Thank you! Regards, Martin
I fly for 30 years and never understood this topic completely, it is often explained by experts with no didactic skills. I completely understand now. Thank you so much for your talent and skills to teach!
Glad I could help! - Martin
Great Video!!! looking forward to more videos from your channel. You can never have too much good information when it comes to flying!
Thank you, Gary! - Martin
Martin, Always enjoy your videos as I fly an A36 too. First one I saw was when you flew into SFO.
wow this is awesome! very very well made. it couldn't be more true that being able to teach someone about a certain topic means you have really mastered whatever that topic is.
Thank you, Jeff. - Martin
This is hands down one of the best videos on this topic! Great job Martin!
Thank you, Vitus. - Martin
Martin - Great video. I have watched some of your other vids, but this one convinced me to subscribe. Your production quality is not too shabby either. Also, adding the out takes was a nice touch.
Thank you, glad to hear you found it useful. And yes, everyone seems to like the outtakes. :-) Enjoy your Sunday!
Thank you, Martin, for this excellent explanation of fuel mixture and running LoP vs RoP. I'm just learning how to fly and appreciate you're ability to explain this subject matter so clearly!
Glad I could help you make sense of it, Alvaro. Good luck for your flight training! - Martin
Thank you. First time that someone is finally explaining this clearly and understandably! Well done.
Thank you, Maarten - glad you found it helpful. - Martin
Beautiful video Martin Pauly, with great insight and nicely explained. Thank you very much.
Thank you. - Martin
Thanks Martin. You did a fantastic job. This is the best explanation I've seen of LOP / ROP operations and protocols.
Thank you very much, John.
since flightsim 2020 i learned so much about aviation thanks to people like you who make these really awesome and easy to understand tutorials and lessons. thank you so much!
My pleasure! - Martin
Awesome video!!! Thank your so much. This is the first time I actually understood what LoP and RoP is and how to set it correctly. Couldn’t believe there where so many outtakes since your speaking is so clear and continuous. Very well done over all!
Thanks, wolleyw! Glad to hear you liked it.
Great video. I like how you walked us through it in the airplane and then explained it on the charts. Very good.
Thank you, Thomas! - Martin
Important information professionally presented in understandable manner. Much appreciated.
Thank you, Jose. Glad to hear you found it useful.
Well explained... Loved the bloopers. Thank you
Thanks, Stephen. Glad to hear you liked it.
Excellent video Martin. Was thinking you weren't going to cover dissimilar mixtures per cylinder, but you did. Really thorough.
Thank you, Andy. Glad you liked it. Regards, Martin
Great video! Really helps with understanding. You made very clear points and had great references to back it up and make it even easier! Thank you!!!!
You are welcome, Aaron. Glad I could help with making this topic clearer. - Martin
One of the best GA videos I've seen. Brilliant!
Thank you, Tomias. Glad you like the video.
Thanks for the clear explanation this helps a lot of us for understanding LOP OPERATIONS.
You are welcome, Mark - glad to hear you find it helpful.
Best video I’ve seen yet on the topic. Thank you so much for this. Very easy to understand.
Thank you! - Martin
Thanks for this thorough LOP explanation. I’m transitioning into an S35 with a similar Gami set up. Very helpful.
Thanks, Erik. What you see in the video (from my A36) will apply pretty much directly to your S35 - a great, fast airframe, by the way. In case you're at Sun 'n Fun this year (April 2019, Lakeland FL), I'll be giving a couple of presentations on the LOP and mixture management topic on Friday and Saturday. Regards, Martin
Great video! Absolutely loved it and was frankly quite excited when I saw the title. Keep it up, I very much appreciate your content!
Thank you very much!
This is a great lesson. I love that you take your time and do your own experiments in the airplane. Great stuff!
Thanks, Jon. - Martin
Love the Outtakes Martin!
Everybody does, Kent 😁 Best, Martin
Martin, great job. The most concise presentation I have seen or read on the subject. I worry about the red box particularly on climb fuel flow management. Great work! Dennis
Thank you for the kind feedback, Dennis. It's good to think about the red box when flying, but keep in mind that it doesn't have the kind of hard, abrupt edges I showed in the video. The concept of the red box should help you realize where the high pressures and temperatures are; how far exactly you stay away from the worst is a large gray (or maybe pink in this case?) area.
Wow! Thank you so very much for this video. As a fairly new pilot, this answered every single question I've ever had about mixture settings with respect to EGT and CHT.
You are welcome, Lee. It's not really a complicated topic, but one which we don't teach very well in primary training. Best, Martin