  I develop a method for assessing the ability of an instrument, coupled with
an observing strategy, to measure the angular power spectrum of the cosmic
microwave background (CMB). It allows for efficient calculation of expected
parameter uncertainties. Related to this method is a means of graphically
presenting, via the ``eigenmode window function'', the sensitivity of an
observation to different regions of the spectrum, which is a generalization of
the traditional practice of presenting the trace of the window function. I
apply these techniques to a balloon-borne bolometric instrument to be flown
this summer (MSAM2). I find that a smoothly scanning secondary is better than a
chopping one and that, in this case, a very simple analytic formula provides a
good (40\% or better) approximation to expected power spectrum uncertainties.
