I just obtained an older Pentax Spotmeter. I think this is a "21/1" unit. Inside the display, there are what appears to be two scales, a high and a low scale. The button on the front of the meter has a big "L" on it. I assume that the "L" means "low". How do I take a reading on the "high" scale? If you can help with this that would be great. Thanks Michael Holley