CHANPHA> change [<systematics>]
This command changes a pha_data package into a pha_per_sec and a pha errors package. The pha_per_sec is calculated by dividing pha_data with the
active integration time. The errors are calculated as the square root of
the pha_data. If a systematic error is given (a fraction of pha_data), then
it is added quadratically to give the total error, which also is divided
by the integration time.