  We investigate differences in Spitzer/IRAC 3.6 and 4.5micron photometry that
depend on observing strategy. Using archival calibration data we perform an
in-depth examination of the measured flux densities ("fluxes") of ten
calibration stars, observed with all the possible observing strategies. We then
quantify differences in the measured fluxes as a function of 1) array mode
(full or subarray), 2) exposure time, and 3) dithering versus staring
observations. We find that the median fluxes measured for sources observed
using the full array are 1.6% and 1% lower than those observed with the
subarray at [3.6] and [4.5], respectively. Additionally, we found a dependence
on the exposure time such that for [3.6] observations the long frame times are
measured to be lower than the short frame times by a median value of 3.4% in
full array and 2.9% in subarray. For [4.5] observations the longer frame times
are 0.6% and 1.5% in full and subarray respectively. These very small
variations will likely only affect science users who require high-precision
photometry from multiple different observing modes. We find no statistically
significant difference for fluxes obtained with dithered and staring-modes.
When considering all stars in the sample, the fractional well depth of the
pixel is correlated with the different observed fluxes. We speculate the cause
to be a small non-linearity in the pixels at the lowest well depths where
deviations from linearity were previously assumed to be negligible.
