I am making a price list based on supplied figures. I would like to add a
markup on every number in every field. To do this successfully I would need
to input a number into each cell and have that individual cell increase by a
set amount and display the new figure. That way I can press tab input a new
figure into the next cell and repeat this process for an entire spreadsheet.

or alternatively (or in addition to),

If I was to have a spreadsheet with the original figures, then highlight the
entire spreadsheet and in one action increase every figure by a set amount
that might be even more convenient.

The markup would be a set figure not a percentage but I could do with
knowing how to do both.

Regards,
Glen