All the drawing packages and stuff only really help if you know what you are looking at... I've seen plenty of random ellipses draw on pictures to "show" the tiller is good. You need to get your eye accustomed to seeing the curve, an app etc is no substitute... IMO the best aid is probably video of it being flexed. The curve drawing rarely shows something I can't see already but is handy for showing it to someone else who probably couldn't draw the curves right themselves!
Del