detrend - SEMI-COMPLETED

For the UVB-VIS arm we will often need to scale the master-dark frame to match the exposure time of our science/calibration frame. If this is the case than the master-bias frame needs to be subtracted from the master-dark frame before scaling. However, if the master-dark frame has the same exposure time as your science/calibration frame then it can be subtracted directly from frame as this serves to remove the bias and dark-current contributions simultaneously.

This logic is all housed within the detrend method.