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pivot points in our calculator dont match

i am using metastock professional.
the pivots in metastock dont match with pivots in our pivot point calculator.
suppose previous days stock futures
open 539.85
high 554.70
low 536.90
close 549.45
the pivot point as per metastock is 546.80
while as per calculator it differs and dont match with any of our formulas.
the pivot point those of metastock our very perfect.
why this happens
please help
What is the formula that metastock use for their pivot point calculation? I assume that metastock have many formula available that can be used with their charts so there are probably a few different versions of pivots for metastock as there are for all charting packages...