With the order you specified, it's quite easy.

Select the cells you want to tab between (eg A3:B5), then go to
FormatCellsProtection, deselect the Locked checkbox then click OK.
Go to ToolsProtectionProtect Sheet. In the dialog box you will be offered
the option to set a password. This is optional. Depending on the version of
Excel there may also be the option to specify what operations users can
carry out. For the purposes of this exercise, the defaults will do. Click
OK.
Tab will now move to the next available unlocked cell working along the row
before moving onto the next row.

The cells do not have to be in one group, but will always check an entire
row before going onto the next row.

--
Ian
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"Frans" wrote in message
...
How can I determine the taborder in an excel sheet ? It needs to go from
a3 to b3 tot a4 to b4 to a5 to b5 etc.