PROCEDURE: 6h

TITLE: Long darks

CATEGORY: Calibration

PURPOSE: Measure darks with long enough exposures to get significant
counts. 

FREQUENCY: Run over range of nominal operating T.  Use as filler when
not doing anything else.

DETECTOR: HRC

PREREQUISITES: none

HARDWARE REQUIREMENTS: none

SOFTWARE REQUIREMENTS: standard statistical analysis tool
                       stsdas.hst_calib.ctools.msbadpix (or IDL equiv)

COMMAND MODE: PSTOL

PROCEDURE/EXPOSURES:  
	1.    bias                         0s
	2.    dark			3600s  (repeat as needed)
	Note T_env, T_CCD at beginning, end and in the middle of each
	   dark exposure.  

TOTAL EXPOSURES: 2

TOTAL TIME: setup + 3600s + 2*overhead = 1.23 hr
	(+ 1.03hr for each additional dark)
	(setup = 10min, overhead = 2min)

ANALYSIS: 

(1) Subtract overscan or master bias.

(2) Run basic statistical analysis tool.  Gives dark count rate.
Compare with previous darks to check if rate & shape remain constant.

(3) Plot dark rate vs. T_env, T_CCD, time.  Note trends.

(4) If more than one dark, combine and identify bad pixels.