In a message dated 3/7/08 12:01:28 AM, Butch writes: > It's simply a small magnet epoxied to the > inside of the gypsy and a sensor that detects each time the gypsy rotates > and > calculates the amount of chain taken in and let out. Does anyone have any > experience with this or any other chain counter? > No experience with this as a chain counter - but, this is the way all modern electronic bicycle speedometers work. A magnet is affixed to the wheel which passes by a pickup on the bicycle fork each rotation. The speedometer head counts the number of revolutions and multiplies it by the circumference of the wheel to calculate speed, distance, etc. These devices have proven extremely reliable, are waterproof, and contain and internal battery which powers the tiny computer for years. I've used one of these devices to measure the RPM of my propeller shaft and estimate boat speed by persuading the speedometer head to accept the calculated advance of my boat for each propeller rotation as the hypothetical bike wheel circumference. Larry Z ************** It's Tax Time! Get tips, forms, and advice on AOL Money & Finance. (http://money.aol.com/tax?NCID=aolprf00030000000001)