Pretty simple, really.
First make sure the unit works...
Check the sensitivity control:
- Place the probe under the enlarger with no negative;
- Set the 5-10-20 switch to 5;
- Turn the sensitivity knob to the max;
- Adjust the aperture and head height so the needle indicates the minimum time on the scale;
- Turn the sensitivity down and see the needle swings freely;
- Repeat for the 10 and 20 switch settings, the sensitivity control will need to be lowered with each change of the switch;
- When switching ranges the needle should indicate the same time on both scales.
To check the the range switch:
- Set the switch to 5, adjust the aperture and sensitivity control so the needle is centered on the '5' scale, raise or lower the enlarger head if needed;
- Close the aperture one stop, the needle should indicate 10 on the '5' scale;
- Turn the switch to 10, make sure the needle points to 10 on the '10' scale;
- Close the aperture 1 stop, make sure the needle indicates 20 on the '10' scale;
- Set the switch to 20, the needle should indicate 20 on the '20 'scale.
To calibrate for a specific paper:
- Make a just-not-white print with no negative - stop the lens down as the time should be around 7 - 15 seconds;
- Place the probe under the enlarger - all safelights need to be off;
- Set the range switch on 10, twiddle the sensitivity knob until the needle points to the time you used to make the print;
- Note the sensitivity knob setting - this is the speed/sensitivity to create a just-not-white tone on that paper;
- If you are out of range then use the 5 or 20 switch/scale;
- If you use VC filters then you should meter with no filter but make the print with a filter.
- You can repeat for any tone you wish. A paper will have a sensitivity setting for every tone it can produce.
- A step tablet can let you find the sensitivity settings for a wide variety of tones with just one print.
- Place the probe where you want your white point to be - or any other tone for which you know the sensitivity setting;
- Set the sensitivity knob appropriately;
- Read the time from the meter, adjusting the 5/10/20 knob to let you use the most readable scale - ie, the needle towards the middle of the range;
- Adjust the aperture up or down if you want more or less printing time.