Default: Exp start - exp start
By default Promote Control measures Bulb Ramping intervals from start of one exposure to the start of the next exposure. This ensures constant speed for the resulting video. However, in some circumstances it may be easier to use "Exp end - exp start" intervals. In that mode Promote Control will measure the Bulb Ramping interval you set from the end of an exposure to the start of the next exposure. This eliminates interval overrun problem (since the exposure time is not subtracted from the interval time), but may lead to faster resulting video playback as your shutter speeds become longer.