ORIGINAL: Dr1Driver
I'll buy the reference line idea. However, since 99% of my planes have 0-0 thrust, the thrust line is usually the datum line.
Dr.1
That may be the case with your own particular models, but it is most certainly not the case with the majority of others. Virtually no standard trainers, for example, have the thrust line coincident with the reference line -- they invariably have down thrust.