  Several calculations in conformally static spacetimes rely on the
introduction of an ultrastatic background. I describe the general properties of
ultrastatic spacetimes, and then focus on the problem of whether a given
spacetime can be ultrastatic, or conformally ultrastatic, in more than one way.
I show that the first possibility arises iff the spacetime is a product
containing a Minkowskian factor, and that the second arises iff the spatial
sections are conformal to a product space.
