Review on Stay Ahead of the Game with the Waterproof Wireless Bicycle Speedometer - LCD Display & Multi-Functions by David Gill

I had never installed anything like this and wasn't quite clear on the instructions so I had to search for the installation. The kit contains 3 round batteries. You have to use 2 at a time: 1 for the LCD, 1 for the sensor. The sensor is opened by sliding; There is no hinge or latch. My little brain couldn't figure out how to do it - I almost broke it trying to open it. But it opens. Once opened, turn the sensor upside down so that the round battery cover falls out. The thin puck also falls out. Be sure to put both of them back in after installing the battery. The magnet fits nicely at the point where the spokes cross on the wheel. The risk of slipping is lower. The arcuate design of the sensor should face outward (not towards the wheel). The sensor should be on the fork and facing the front of the wheel. The magnet must be held very close to the top or bottom of the sensor's wide, flat surface. This works on my Mongoose bike with fat tires. I can only use it at night so the photos are hard to see but they show how I set it up. I didn't have the patience to roll a hoop on a short roulette to get a number to program the device, so I got down to basic math. Wheel circumference = diameter x 3.14. Near enough. Perform metric conversions as needed. Much luck!