Different Between Intraday and Daily Data?

[Bob Fulks <bfulks@xxxxxxxxxxxx>]

Does anyone know why the high and low values on a daily bar of the 
DJIA are so different from those you calculate from intraday bars?

For example, on the attached GIF, the red and blue traces are the 
high and low respectively, from the previous daily bar. The gray 
lines are the values derived from the intraday bars for the previous 
day. The range of the intraday bars is much less than that of the 
daily bars.

My numbers for 3/6/01 from two sources:

              Open     High       Low      Close

Daily      10570.17  10759.40  10508.43  10591.22  Yahoo 
Daily      10570.17  10759.40  10507.21  10591.22  Dial Data

Intraday   10578.3   10690.6   10576.0   10589.8   BMI
Intraday             10690.71  10576.05            QuoteCom

Diff           8.13     68.80     68.79      1.42

The open and close are pretty close and I understand that they make 
adjustment to those. But why should the high and low be so different?

Thanks.

Bob Fulks

Attachment: Description: "DJIA3.gif"