  The physics that determines the line shape of the 1S--2S transition in
magnetically trapped $\bar{\rm H}$ is explored. Besides obtaining an
understanding of the line shape, one goal is to replace the dependence on large
scale simulations of $\bar{\rm H}$ with a simpler integration over well defined
functions. For limiting cases, analytic formulas are obtained. Example
calculations are performed to illustrate the limits of simplifying assumptions.
We also describe a $\chi^2$ method for choosing experimental parameters that
can lead to the most accurate determination of the transition frequency.
