I was suprised to note that an inter-dependency developed between different
sheets, which do access the same data, but none of which changes that data.

For example: Sheet1 and Sheet2 both access data on Sheet3. Neither Sheet1
or Sheet2 modifies the data on Sheet3. However the simple act of entering
new data in Sheet1, which causes Sheet1 to access data on Sheet3 (without
changing Sheet3), forces a "Worksheet_Calculate" event on Sheet2 - the
reverse is also true, any change on Sheet2 forces a "Worksheet_Calculate"
event on Sheet1.

I would have expected the "Worksheet_Calculate" events of Sheets1 and 2 to
remain independent.

Notes:
The "Worksheet_Calculate" event for Sheet3 does not occur.

Sheets 1 & 2 utilize the "Today()" function

Sheet2 has a Chart who's source data is on the same sheet.

Sheets 1 & 2 utilize UDF's, but they do not share any UDF's, nor do the
UDF's affect any changes to any common source data.

Does anyone have any comment as to whether this inter-dependency between
Sheet1 and Sheet2 is normal?