There is now an iPhone app to check your tachometer. It is called "Engine RPM"
and it is in the Utilities category in the App Store. It uses the sound of the
engine to determine RPM as accurately as an optical tach. It works on any
engine that makes noise: small planes, motorcycles, R/C models, etc.

This app is based on our "RPM from Sound" freeware Pocket PC app that has been
available for years. But this iPhone app is more reliable, easier to operate,
and covers the range 500 to 90,000 RPM.

Robert Scott
Real-Time Specialties
Ypsilanti, Michigan