User-defined variables.
Are you sure you will remember all figures when you really
need them? Can you memorize hundreds of values (tax, currency, bank rates or salary of
your 100 employees)?
Just create "user-defined variables" containing these values and use them in any
calculation you need. Click "Insert variable" button when "expression"
cell is active in your calculation. The list of user-defined variables will appear:

To add a new variable, click "New". By default the
list is read-only. When you click "New" button, a blank record will appear in
the list, and you'll be able to change its value. To edit variables and their values,
click "Edit" button. Any changes will be allowed.
Select the needed variable from the list and click "Ok". The selected variable
will be inserted into expression line of your current
calculation. Its value is now available in your calculation.