Pentax 645N questions

I bought a used Pentax 645N and have a couple quick questions....

How do you change the ISO?

What does the little switch on the left side below the PC plus do?

Is there a focus lock button that I'm missing?

-rob

Unless things have changed Pentax USA keeps all old manuals online for free download. When I mean all I mean right back to the 1950s.

To change the ISO, there's a lever on the left that looks like the bottom of the knob. Push that 'til the white line is at "ISO", then use the arrows on the top on the right to adjust it. Did that make sense?
I really don't know what the lever on the side does - I can look it up if I can find my manual. It's possible that the "ML" button on the back of the right grip is the focus lock, but I don't know. I can look that up, too.

OK, the "ML" button is for memory lock. There isn't a specific button for focus lock - you simply focus on your subject, keep pressure on the shutter, recompose, then depress fully to shoot the frame.
The lever on the side is to do multiple exposures. Before the first frame, push the lever up until it clicks into place, shoot the first frame, then move the lever back to its normal position and shoot the next frame. The film will not have been advanced between the 2 frames.