Oxidation Reduction Potential -- HELP

[hamop78]

[Full original thread moved to the China Shop -- PoolDoc]

I've been watching this and other forums for a while and I finally found the need to register and "ask the experts"

Here's the deal --- I got an instrument to read pH, which had ORP as an additional capability. After 3 different instruments all Extech PH220-C (2 bad ones) I have one that appears to read something in mV.

My pool is crystal clear, here's the specs as of tonight.
Temp 85F
pH 7.54 (calibrated electronic & titration)
FC 7.0 ppm (FAS-DPD)
TC 7.0 ppm (FAS-DPD)
CC 0 ppm (FAS-DPD)
TA 90 ppm (by titration)
CH 230 ppm (by titration)
Phosphates <100 ppm (titration)
CYA 60 ppm (25ml sample using 0013 reagent)

I am using a modified BBB (using up a bucket of Cal Hypo substituting 12 oz Cal hypo per recommended gallon of bleach)
I haven't had any pucks in for well over a month.
I used a small amount (2lb) of Potassium Monopersulfate a couple of weeks ago (more stock to use up)

Here comes the question ----
My ORP is reading negative 19mV

With my pool being nearly perfect (IMHO) how can that be??? I figured I should be in the 650 - 750 mV area. I have not used any reducing agents, and from everything I have read (many internet pages)--- my treatments should not be affecting the ability to display a proper mV reading.

Any help -- Ben, ChemGeek, Waterbear, ANYBODY!!!!!