  Long-term stability of deformable mirrors (DM) is a critical performance
requirement for instruments requiring open-loop corrections. The effects of
temperature changes in the DM performance are equally critical for such
instruments. This paper investigates the long-term stability of three different
Iris AO PTT111 DMs that were calibrated at different times ranging from 13
months to nearly 29 months prior to subsequent testing. Performance testing
showed that only a small increase in positioning errors occurred from the
initial calibration date to the test dates. The increases in errors ranged from
as little as 1.38 nm rms after 18 months to 5.68 nm rms after 29 months. The
paper also studies the effects of small temperature changes, up to 6.2{\deg}C
around room temperature. For three different arrays, the errors ranged from
0.62-1.42 nm rms/{\deg}C. Removing the effects of packaging shows that errors
are $\le$0.50 nm rms/{\deg}C. Finally, measured data showed that individual
segments deformed $\le$0.11 nm rms/{\deg}C when heated.
