ICE allows you to pause (``p"), resume (``r"), stop (``S") and abort (``A") an exposure in the midst of an integration. Furthermore, you can change the integration time (``x"), or the title (``t") during an exposure. Since each command is a single key-stroke command (no carriage return is needed), accidentally typing in the data acquisition window during an exposure could have serious consequences. (For instance, typing a flpr with the mouse positioned in the acquisition window would pause (``p") and then resume (``r") an exposure!) Thus we require an exposure to be paused before doing anything else, and the commands that terminate an exposure, stop and abort, require capital letters (``S" and ``A").
To resume the exposure, simply type an r. The shutter will open and the time will begin updating again.
Or you could decide you don't want the current exposure at all. In order to abort the exposure, first pause the exposure with a p and then abort the exposure with an A. The image will be lost, and the exposure counter will not be updated. (Note that the ``A" must be upper-case.)
Note that while you can always shorten the length of an exposure, you can only increase the length of an exposure if the initial exposure length was longer than 5 mins (by default). The user should be warned that an exposure time that has been changed to 30 secs, say, will not be as accurately timed as an exposure that began and ended as 30 secs. This is due to the fact the Unix system, rather than the CCD controller, keeps track of the time if the exposure time is altered. We are uncertain, currently, what sort of error this may introduce; the most pessimistic estimates are 1 or 2 seconds regardless of exposure time. Thus this method should be fine for long exposures, but may be dicey if 1% photometry is needed for short exposures! We recommend not altering the exposure time if 1-2 sec errors in the subsequent timing would affect your results.