US Patent 7131216 Distance measuring apparatus

A distance measuring apparatus having a frame and a wheel rotatable relative to the frame around a first axis. The wheel has a peripheral surface that can be rolled against a surface upon which a distance measurement is to be taken. The distance measuring apparatus further has a counter assembly through which advancement of the distance measuring device can be converted to a distance measurement. The scraper assembly has a scraping edge that is one of (a) adjacent to the wheel, and (b) against the wheel. The scraping edge intercepts foreign matter adhered to the wheel as the wheel is rotated around the first axis to avoid buildup of foreign matter upon the wheel as the distance measuring apparatus is operated.