The measuring principle of TEG (A), ROTEM (B) and ReoRox FOR (C). In the TEG instrument, a pin is suspended by a wire into a cup containing the blood sample. The cup rotates back and forth 4.75° every 10 seconds. During coagulation of the sample, fibrin strands will form between the pin and the wall of the cup which will affect the movement of the cup which is gradually transmitted to the pin. In the ROTEM instrument, the cup is stationary and a ball-bearing pin rotates back and forth 4.75°. The movement of the pin is driven by an elastic spring. Also here fibrin strands will form between the wall of the cup and the pin during coagulation and the strength of the strands will affect the movement of the pin. In the ReoRox, the cup is turned up every 2.5 seconds and then released, allowing rotational oscillation around the longitudinal axis. An optic sensor records the frequency and damping of the oscillation. A pin (bob) is immersed into the cup via a shaft. The fibrin fibres formed during coagulation will couple the cup to the bob, and the amount and activity of platelets bound to the fibrin network, will affect the frequency and damping of the oscillation.