HM-250 and HM-250D Length Comparators are similar units for measuring length changes in 10in (254mm) specimens cast with special gage studs in the ends to fit the bottom and top anvils of the Comparator. Sensitive indicator with 0.0001in (0.0025mm) divisions measures specimen length. Recommended HM-250D has a quick-reading 0.5in (12.5mm) range LCD digital indicator with in/mm switch, RS-232 port, and replaceable 200 hour battery. The analog HM-250 has a 0.4in range mechanical dial indicator, which will convert to time-saving digital version with purchase of a digital indicator. Comparators include a heat treated, hardened Invar Reference Bar for exactly zeroing the dial indicator at regular intervals. Construction is a sturdy upright support attached to a solid base. Test specimens up to a 4x4x10in (102x102x254mm) cross section, but 1x1x10in (25x25x254mm) prisms are normal. Inquire for special adapter and shorter Invar Reference Bar if 5in (127mm) long prism samples are tested.