  One-dimensional (1-D) microlens parallaxes can be combined with heliocentric
lens-source relative proper motion measurements to derive the lens mass and
distance, as suggested by Ghosh et al. (2004). Here I present the first
mathematical anlysis of this procedure, which I show can be represented as a
quadratic equation. Hence, it is formally subject to a two-fold degeneracy. I
show that this degeneracy can be broken in many cases using the relatively
crude 2-D parallax information that is often available for microlensing events.
I also develop an explicit formula for the region of parameter space where it
is more difficult to break this degeneracy. Although no mass/distance
measurements have yet been made using this technique, it is likely to become
quite common over the next decade.
