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prescan: Make a pre-scan to check crystal quality

The "prescan" program can be used to collect a quick first scan to check whether the crystal is diffracting, and whether the mosaicity is within normal ranges.

Usage

The program is invoked by the command line:

prescan [options]

The possible options are:

gui: Makes the program run as a GUI (i.e. it will prompt for all parameters, show a little progress window during the scan, and pop up the measured image in an "ndisp" window).
exposuretime=value: Specifies the exposure time in seconds. The default comes from the indexdegreetime and phichiexposuretime options in the configuration file. Which one is used is based on the setting of the "chi" option.
frameangle=value: Specifies the omega scan range. Default dependent on the configuration file.
chi=value: Specifies the chi scan range. Default "chi=10". Even when the program is run as a "gui", it might be useful to specify the desired "chi" angle ( especially if "chi=0" is desired) such that reasonable defaults can be chosen for other parameters.
dx=value: Specifies the position of dx. Default is dependent on the configuration file.
omega=value: Specifies the central position of omega. Default "omega=180".
kappa=value: Specifies the central position of kappa. Default "kappa=0".
theta=value: Specifies the position of theta. Default "theta=0".
phi=value: Specifies the central position of phi. Default "phi=0".

The measured frame will be stored in the file "pre##f###.kcd", starting from the first scan number for which the "pre##f001.kcd" file does not exist on disk.

Side effects

The prescan command will raise the power on the X-ray generator to the nominal values if it thinks the power is insufficient for a measurement. However, since you normally want to perform a measurement just after, it will NOT set the generator back to a low value when it completes.

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