  We calculate the flux threading the pick-up coil of a square SQUID
magnetometer in the presence of a current dipole source. The result reproduces
that of a circle coil magnetometer calculated by Wikswo with only small
differences. However it has a simpler form so that it is possible to derive
from it closed form expressions for the current dipole sensitivity and the
spatial resolution. The results are useful to assess the overall performance of
the device and to compare different designs.
