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Understanding win.monitorFramePeriod code

I wonder what does it mean:
“frameRemains = 0.0 + 1.0- win.monitorFramePeriod * 0.75 # most of one frame period left”
I want to set precise stimulus exposition but I don’t understand this part with "win.monitorFramePeriod * 0.75 “. Especially confusing is “*0.75” because I am worried about disturbing the exposition time. Based on this example, if I want to get 1 s exposition, shouldn’t be there " frameRemains = 0.0 + 1.0” or “frameRemains = 0.0 + 1.0- win.monitorFramePeriod” ?

 # *text_4* updates
    if t >= 0.0 and text_4.status == NOT_STARTED:
        # keep track of start time/frame for later
        text_4.tStart = t
        text_4.frameNStart = frameN  # exact frame index
        text_4.setAutoDraw(True)
    frameRemains = 0.0 + 1.0- win.monitorFramePeriod * 0.75  # most of one frame period left
    if text_4.status == STARTED and t >= frameRemains:
        text_4.setAutoDraw(False)