Step 1. Find the VBA Editor

Open a new workbook.

Click on Tools, then select Macro and then select Visual Basic Editor.

Step 2 Create a Module.

Now right click in the Project-VBA Project window and select Insert and Module.

If the Project-VBA Project window isn't visible then follow step 2a →

Step 3 Write a Function

You should now have a cursor blinking at you in the window which shows the code for module1.

Step 1a. Enable Macros.

If these menus are grayed out then try selecting Tools, then options.

Then click on the security tab followed by the Macro Security button.

Finally change the security level button to medium. Click okay and return to the worksheet screen. If this doesn't work then your network settings etc might need changed. Seek advice from a computer service droid.

NB. If you now download dodgy Excel spreadsheets from dodgy sources and allow their dodgy macros to run then you can COMPLETELY MESS UP YOUR COMPUTER! so only run content from people that you trust or, better still, write your own dodgy macros.

Step 2a. Find the Project Explorer.

If the Project Explorer window isn't visible then click on View and Project Explorer.

Step 4

Now type the code for the function into the window. The machine will add End Function for you automatically. Excel has comprehensive help files to explain what all the different commands do. The main problem is knowing enough American computer geek speak to guess what they call 'highest common factor' etc. (GCD, work it out.)

You can either type it or cut and paste from below the picture.
You don't need the comment lines which begin with a '. Excel colours things in to differentiate commands, variables and comments.

Function declett(no1)
'converts a decimal result grade such as 6.5 into a standard grade such as 6b.
int1 = Int(no1)
int2 = Int(no1 * 10)
frontbit = int1
backbit = int2 - 10 * int1
If backbit < 4 Then
endbit = "c"
End If
If (backbit >= 4 And backbit < 7) Then
endbit = "b"
End If
If backbit >= 7 Then
endbit = "a"
End If
declett = frontbit & endbit
End Function

Step 5 Test It

To call your function simply enter it into a cell just like a standard Excel function.

Lots of things can go wrong at this point:
If nothing happens when you press Return check that you have got the function typed in absolutely right.
The formula will only work after you have got the function right. It won't go back to cells which had the formula entered prior to you getting it right. So once you have it working apply it to all the cells that need it.

Going Further