pivot calculation open high low close

when i look in my data from the esm7 (esmini) i have difficulty in understanding what open and what close values are used for the classic pivot calulation. the website fills in the open en close for the previous day for which they calculate the pivots but i have different data all together when i look up open and close in my data. what time stamps are used to find the open and the close values. Can anyone help me with that?
kind regards and thanks for your help
skippie

I didn't know that poster - thanks for the update. I do know that I've done considerable research on when the pit is going to disappear and I think that it will be gone (at least in its current form) within the next few years.