This command only becomes available if you have just clicked OK in the Set Calibration dialog, but haven't yet calibrated any images. It generates one master image for each image group created by Set Calibration, and displays them as image buffers. They can then be saved for future use in the Set Calibration command.
The master frames generated by MaxIm DL are pre-calibrated. The master dark frames have been corrected with the most appropriate group of bias images, and the master flat frames have been calibrated with the most appropriate groups of bias and dark frames. Completed calibration steps are recorded in the CALSTAT FITS key of generated images. The letter 'M' is added to this key for all master frames; it indicates that the Create Master Frames command was used to create the image. The letters 'B', 'D' and 'F' indicate that bias, dark and/or flat frames were used to calibrate the image.
This function saves recalculation time and disk space if a set of calibration frames is used repeatedly.