I have an old 2 button Trek Sensor cyclometer. I haven't used it in quite some time. However, it still appears to work and I want to put it on my son's bike. Problem is that I cannot change the wheel size. With only 2 buttons, you'd think it would be easy to figure out. I can change the time. I can change from Km to M. But that's all I can figure out. HELP! Please email to Djhufnagle_aras@hotmail.com.