  In this text, we compare several invariants of the reduced Whitehead group
SK1 of a central simple algebra. For biquaternion algebras, we compare a
generalised invariant of Suslin as constructed by the author in a previous
article to an invariant introduced by Knus-Merkurjev-Rost-Tignol. Using
explicit computations, we prove these invariants are essentially the same. We
also prove the non-triviality of an invariant introduced by Kahn. To obtain
this result, we compare Kahn's invariant to an invariant introduced by Suslin
in 1991 which is non-trivial for Platonov's examples of non-trivial SK1. We
also give a formula for the value on the centre of the tensor product of two
symbol algebras which generalises a formula of Merkurjev for biquaternion
algebras.
