A cheaper version of the Rotolog 500, with fewer scales and made entirely of plastic. The rule was made by concise, and seems like a blown-up cousin to their Model 28. It was a bit of a judgement call to say this is a Sinco rule; the front of the rule clearly labels it as a Concise, but hey. Anyway, it's actually quite a nice log-log rule for being all-plastic. Purchased for $12.95 at the MIT Museum. They probably still have some left. It's worth it.