Formula To Subtract To A Limit ? - Excel and Alert

[andrej309]

Hi

Can someone help me with a issue a am battleling.
I am pretty new to the advance formuals in excel so pleas ebear with me.

This is the scenario
I Created a excel workboot with one sheet.What this file should do is check for duplicates and warn me if i have reached zero.

So,I have One Column with data which i have data validation on to check for duplicates and it actually stops and warn if i receive duplicates.
That is working fine and not my issue.

I want to add a function whereby want to do the following.

• Enter the amount of data i will be populating in column A this is to restrict that it does not go over a the specified mount(I will be scanning Data into the column with a barcode scanner just for intrest sake)
• Then i have a cell with a =COUNTA(A12:A3000) formula to count how much data is in the row as a am populating
• Lastly i did a =Sum(B3-B4) formula to deduct the two cell from each other.

This is wat it looks like

Enter Amout of Tags to be Scanned =500
Total Scanned =5
Total To Be Scanned =495

Value of 500 is Column B3
Value of 5 is Column B4 =COUNTA(A12:A3000)
Value of 495 is Column B5 =Sum(B3-B4)

Here is the question how do i force the Column B5 not to go below zero so that the person know they cannot enter anymore data.

I have tried Data Validation so that i can stop the process and dispaly a warning as i did with the duplication but it does not work.

Firstly can you have multiple data validation in 1 sheet.
Secondly how do i stop the process when the value receaches zero

Any help will be appreceated.

Thanks
PS- Sorry for the Novel