Your spreadsheet may have a macro that performs a re-calc every time a
particular spreadsheet event occurs. It may be set up to occur when
you enter or leave a particular cell or particular range of cells, for
instance.

You can check this by pressing ALT-F11 to open the VBA editor. In the
Project pane along the left margin of your screen, find the VBAProject
associated with your spreadsheet name. There is an icon tree for each
tab in the workbook, and for the workbook: right click on each icon and
click View Code- this is where event macros are stored. The event
triggers will be called something like SelectionChange, Change,
Deactivate, etc. Look for the command Calculate, and investigate the
source and rationale for that macro.