Well DT, I think I pooch-screwed this one up a bit. My answer was based on keying some of the wrong symbols (and time frames) into TradeStation charts with the indicator "Trader Floor Pivots" applied. CORRECTION: the TS pivots indicator is not based on RTH but rather on the data present on a chart.
After going back through things, there was still some funky monkey results though. If charting just RTH INTRADAY using 15-minute bars (TS symbols: ESZ09.D or @ES.D), the mid-pivot number differed from the RTH DAILY bar results ... close but still a different resulting number.
When all trading time is used (TS symbols: ESZ09 or @ES), the 15-minute bar chart mid-pivot value was different by almost a full point compared to the mid-point value generated using DAILY bars with the same exact symbols. And yet the High, Low and Close values displayed were the same on both the 15-minute bar and daily bar charts.
I also did some other comparisons of different intraday charts and sometimes came up with different values displayed for the mid-pivot. The 15-minute bar chart and 1-minute bar chart were about a half a point off for the mid-pivot. They showed different prices as the "close" at 23:59 ... didn't see any intraday variances between different bar times (15min, 1min,77min etc.) using RTH.
Using a chart of DAILY bars for all trading hours showed the SAME PIVOT NUMBERS on TradeStation and on Mypivots for Thursday 10-22-09. So there's the match-up I guess. Good lord this is the most convoluted thing I've ever written.
Anyway, maybe this sheds some light on things. Additionally, I popped open the TS Easy Language code for their pivot indicator ... and this is it:
Resistance Level 3 = R3 = R2 + YestHigh - YestLow
Resistance Level 2 = R2 = PP + YestHigh - YestLow
Resistance Level 1 = R1 = PP * 2 - YestLow
PivotPoint = PP = ( YestHigh + YestLow + YestClose ) / 3
Support Level 1 = S1 = PP * 2 - YestHigh
Support Level 2 = S2 = PP - YestHigh + YestLow
Support Level 3 = S3 = S2 - YestHigh + YestLow
The pivot formulas for the mypivots site are at:
http://www.mypivots.com/investopedia/46/classic-pivot-points
Btw, tick charts can show slightly different results for the pivot indicator in TS also.
And I've seen scads of different variations on calculating these. Feel free to Google yourself to death for pivot formulas. I'm all worn out ... my brain hurts and I'm about to start clawing my eyes out. Goodnight.