Extending the film advance lever to activate the meter with half press of the shutter. I suppose the thought process was that this would prevent battery drain when a camera is in a bag and something may contact the shutter accidentally. Of course this method tends to poke into the eyes of those who are left eyed. A more clever implementation can be found in the Pentax MX and LX (possible others too?) that have a shutter lock to prevent accidental activation of the meter or shutter. Also, the meter can be activated and the shutter can be fired without the film advance sticking out.