Excel 2007 : Display Percentages less than 1%

I have a column on a spreadsheet where the cells are formatted to display percentages - related to floor space used for different purposes in a building.

This allows the user to enter a value, eg. 25%, 10% etc. However, there are instances where the value entered is less than 1%, which is where my problem lies.

Because I need to be able to total the percentages I need to prevent the user from entering things like <1%. I have achieved this using the Data Validation Custom Formula, =ISNUMBER(Cell Ref) and coupled this with a warning, "Please enter an actual percentage".

But how can I allow the user to enter values such as 0.5%, 0.1% etc. If the user enters these values, the cell displays 50% and 10% respectively, whereas I need the cell to actually display 0.5% or 0.1%.

Many thanks

I should have added 'other than asking people to enter 0.005 for 0.5%.

Is there a way to allow users to enter 0.5 and for excel to display this as 0.5%, whilst still allowing the user to enter 10 and excel display this as 10%?

It appears as though you actually have to enter 0.5, rather than .5. This is where I was going wrong.

If you enter .5 then it will appear as 50%, however if you enter 0.5, it will appear as 0.5%. Is there any logic to this?