Transponder on our 152 has a simple timer; Start, Stop & Clear, this is just about all I need for Nav ex. Failing that, I have a timer on the iPhone, I have never used this in flight but suppose it would do the trick. Failing that, (must be a bad flight!) I have a watch; not as precise admittedly but should do the job also. Can't see how you would justify the need to purchase a timer for PPL training in my humble opinion.
