But if it goes fully to the right, it means it's past the range. Try switching to 90dB. If it still goes all the way to the right, go to 100 on the switch.
The analog meter is good for about +/-6dB from where you are measuring. Ie., 74~86 when set to 80. If you are in the high 80s, change the setting to 90. The digital meter is good to about the same range, maybe 1dB more. But if you get 87dB when set to 80, set it to 90 and you may get a reading of 86dB.
If you want to find the peak SPL, and not just the level to calibrate, set the meter to FAST and MAX. Set it to SLOW when you want to even out the average SPL and calibrate.