[R-390] Ramblings on Calibration - was: HP 8640B

[DJED1 at aol.com]

Boy, you guys put me to shame.   I was going along, setting the R-390A to 
WWV, and thought 100 HZ was close enough.   Then I got the 8660 signal generator 
and figured out how to measure the beat note so I could read frequency to 1 or 
2 Hz.   Now you tell me that 0.1 Hz is only OK accuracy!   And frequency was 
the one thing I was doing good on- accurate to 1 part in 10^7.   On my 
voltmeters, I was going by the consensus method: if two of them read the same then it 
must be correct.   The trouble was that the two that agreed were a precision 
power supply that I got from a garage sale for $5, and a Radio Shack digital 
VOM from a similar source.   I finally borrowed a calibrated Fluke (0.025% 
accuracy on DC) from my son's shop and verified the the power supply and VOM were 
indeed correct to 0.1%.   Also verified that my H-P 400E was still good to 1% 
on AC volts.   Fortunately, I calibrated my scope to the power supply, so it's 
good.   And I used the scope to set up the URM-25, so it's good.   Now if I 
could only get some precision caps and resistors to calibrate the rest of the 
VOM I'd be all set.
Ed