Let K = Q() be a
pure quartic number field, where D and d are natural numbers such that d divides
D3 and d is fourth power free. Then 𝜀 = ±(+ D)∕(−D) is a unit
of K whose relative norm to the quadratic subfield of K is 1. We consider
the condition for 𝜀 to be a member of a system of fundamental units of
K.