What about it? They were very popular (and relatively cheap) back in the 70's and early 80's. They came in a couple of different formats, the clicker like you have seen and some that had a small pulley that was mounted on the wheel with a rubber drive belt that drove the meter. IIRC they came in different sizes for different sized wheels...I know the belt drive ones (Huret was the most common brand) came with a different sized drive wheels to use for the different wheels sizes.

Aaron