Force excel to only accept 10 digits

Hi, attached is a spreadsheet im working on for a charity organisation and there are 2 columns which are set aside for phone numbers and I have already ensured the correct formatting is in place. My question is, how do I force the user to enter exactly 10 digits and not (for example) 8 digits which is how some people may write the 'Work' phone number for example.

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Qlemo"Batchelor", Developer and EE Topic AdvisorCommented:
Well, those phone numbers have exactly 9 valid digits. You are adding the leading zero making it 10 digits.

The soft method is to use conditional formatting checking for values below e.g. 10 000 000, and using a different cell foreground or background color.
Changing the foreground color can also be achieved in the format option, e.g. with
   [>=10000000]0### ### ###;[Red]0### ### ###
(for Mobile).

The restrictive way is to use Data Validation (in Data Ribbon). Invalid values are prevented that way.

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recycleausAuthor Commented:
Data validation was what I was looking for... thanks
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