1. Use a PHOTOVOLT 577 in the LOW gain position with the “Y” search unit and a green tristimulus filter*. Allow the meter to stabilize for about 30 minutes.
2.  Press the G (Green) button on the 577.
3.  Zero the 577 by placing the BLACK CAVITY STANDARD over the light source opening and centered so that no room light leaks under the edges. Press CHANGE and ZERO. The display will read 0.0 or .0.
4. Remove the BLACK CAVITY STANDARD and place the STANDARD PLAQUE over the light opening. Press CHANGE and STD (STANDARD) on the 577. CHANGE and STD lights will be on.
5. Press the A (Amber) button on the 577 to change the first number on the display to correspond to the first number on the STANDARD PLAQUE. Press the B (Blue) button to change the second number on the display to correspond to the second number on the STANDARD PLAQUE and the G (Green) button to correspond to the third number. Press STD to store these numbers in the memory.
6. The system is ready for reflectance measurements of the filter pads.
7. Remove the STANDARD PLAQUE and replace with samples according to ASTM D-6468-99.
8. It is good practice to zero the 577 frequently by placing the BLACK CAVITY STANDARD on the light opening before and after a series of measurements in the same manner as in (4) and (5) above.

* A “T” search unit with a green filter can also be used. The green filter of the “T” unit is identical to the green filter of the “Y” unit. If using a “W” search unit, use HI (HIGH) gain.