Thanks, Charles. > The board should have a part number etched in copper, of the form > "0xxxx-yyyyy". "xxxx" should be the instrument model number. 08770-yyyyy is etched in copper => 8770A Arbitrary Waveform Synthesizer. 8770A spec: REFERENCE OSCILLATOT (10 MHz Quartz) Aging rate < 5 x 10^^-10/day Makes sense. Ulli