We have 2 piston cylinders (about 2 foot diameter x 4 foot height) that have a 6 inch stroke. We were having these cal'd at UW for as long as I can remember. Anyway, I've been asked to research a new vendor. The UUT raised to 1.5 inch stroke, is set on the lower platen, the upper platen is lowered on top and slowly increased to 1.8 Mlb in 200 klb increments. Pressure gages in the hydraulic circuit are recorded and compared with the calibrated compression. We then calculate a BFSL. As far as accuracy, the UW machine is ±24 klb, I'm not really sure what accuracy we need, right now I am looking for capabilty, NIST traceability of the cal standard, etc. etc. I have a call into Instron and will contact Tovey and Morehouse tomorrow. Any ideas would be appreciated.