Thromboelastography (TEG) and rotational thromboelastometry (ROTEM). The following is a helpful description of the similarities and differences between the two. “Whole blood (a minute amount of it, no more than 1 ml) at body temperature (37º) is added to a heated cuvette (a little cup). A pin is suspended into the cup, and then some sort of rotation takes place. In fact the main difference between TEG and ROTEM is the bit which rotates (TEG rotates the cup, and ROTEM rotates the pin). Irrespective of which bit is rotating, some impediment to the rotation develops as the blood clots. The degree of this impediment is recorded as “amplitude”, and displayed on the time vs. amplitude graph.” An example of the type of graph generated by these instruments is shown here (the details are not important in the context of this short answer).