Apple Macintosh Performa 577 - Manual (Page 145)

Adjustments Light Meter Setup - 24
readings, verify the
readings with a known-good
light meter or photometer.
Also check the age of the R77
light meter by its four-digit
manufacturing date stamp
(such as 0398 for March
1998).
Caution:
Dropping the
meter can permanently
damage its accuracy. A
shock-damaged meter might
read incorrectly or its
pointer may not drop to
zero.