1. Preview button

You can see images at the maximum aperture throught the viewfinder when you use a Nikkor Auto Lens.
With this button, you can see the rough resulting image through the viewfinder.

2. Memory system of metering value

Use this in the situation like you are hard to get the correct exposure of such subject as unstable one.
The lever is used both as the memory system and the self-timer and while shooting on aperture-priority, push the lever in the direction of the camera center, which sends the metered value to the circuit to memorize the information.
The memorized information maintains till you let go of the lever.

This is all for Nikomat EL and thank you for taking your time to see this.