Abstract: Blood clot analysis instrumentation used to evaluate platelet function and clot structure by monitoring force development during clot retraction or upon application of a known amount of force can have a calibration check automatically performed by using a top member with a known amount of mass which is detachable from the instrumentation, and preferably is a disposable component. The calibration check is performed by monitoring force or displacement on a holding member with and without the top member attached. If the difference measured is within a preferred tolerance range, then the instrumentation can be deemed to be within the specifications deemed best suited for the instrument. The top member may also be modified to allow for mixing reagents with the clot, thereby avoiding the need to pre-mix blood with reagents before measurement.