META.
brown_eyes, I have just updated my old twin training approval notes from many years ago. The standard you wish to achieve can vary from the average to that well above what is required. The web has lots of very good info and by just cutting and pasting and using power point an extremely good brief can be put together.
I also have a very good Range and Endurance brief using Geometry, Trigonometry, a host of Graphs to explain the subject, together with performance tables for both a single and twin engine aircraft to support those briefs. You can have it for nothing, PM me. By the way you don’t need hundreds of hours to put those briefs together any person with a modicum of intelligence can do it in a few days.