Dependant? Data Validation

Hi all

I am sure there is someone out there who knows how to do what I am hoping to achieve.

I don't know how to get a data validation (B1) to be dependant on any figure being entered into a cell to the left of it (A1).

For Example:

Column A Column B Column C

Row 1 ##,### Drop down Calculation dependant on drop down


A1 - will have a value entered.

B1 - I would like the action of populating A1 to prompt the user to select from a list of 4 items in a dropdown list in B1, i.e. the user will not be able to continue onto next row until the selection has been made.

C1 - This will be a percentage calculation e.g. IF A1="High"*75%

I have worked out the calculation formulae, I just don't know how to get the data validation (B1) to be dependant on any figure being entered into A1.

I hope my explanation is ok and that someone can help me.

Kind regards