  Usually, equal time is given to measuring the background and the sample, or
even a longer background measurement is taken as it has so few counts. While
this seems the right thing to do, the relative error after background
subtraction improves when more time is spent counting the measurement with the
highest amount of scattering. As the available measurement time is always
limited, a good division must be found between measuring the background and
sample, so that the uncertainty of the background-subtracted intensity is as
low as possible.
  Herein outlined is the method to determine how best to divide measurement
time between a sample and the background, in order to minimize the relative
uncertainty. Also given is the relative reduction in uncertainty to be gained
from the considered division. It is particularly useful in the case of scanning
diffractometers, including the likes of Bonse-Hart cameras, where the
measurement time division for each point can be optimized depending on the
signal-to-noise ratio.
