filter grade

This filter is for missions with CCD detectors whose events are assigned a grade (or pattern). The grade can be specified as a single number (eg 0), a range (eg 0:2 or 0-2), an upper limit (eg $<$ 4), or a lower limit (eg $>$ 3). Specifications should be separated by commas (eg 0,2-6) and enclosed in double quotes if given on the command line instead of when prompted.