Ok, I just received my 12 function Schwinn computer. I noticed that someone was having trouble finding the button battery LR43. I found them at Harbor Freight. I bought a 24 piece button battery kit for $5. It has six different size batteries in the package. There are 4 of the LR 43 batteries. And a lot of common batteries for watches and other stuff. Also the least functions for me the better. I just wanted a simple one. So with only two buttons and 12 functions I thought I would try it. For $10 this is a very good deal. It seems very well made and solid. It locks onto the holder very tightly and feel secure. Before I installed this I sat down and read the instructions twice and set it Up before I installed it on the bike. Just take your time and look it over very closely all the parts. The arrow on the sensor is obviously where the magnet should pass by. The battery cover is very well made and solid. It has a "O" ring to waterproof it from the rain. The instructions do not list all the tire sizes. With the calculations mine came out to be 2055 for a tire size of 26/1.95 hope this helps.