i need help creating a stock control system

[Guest]

i have a spreadsheet with4 coloums, they are, product, price, quantity,
stock. for the stock control to work when i type in a number in the quantity
the stock will be deducted by that amount. howvever when i did this everytime
i deleted the number in the quantity coloum the stock changed back to its
original number which was 100. i was wondering whether there was a way for
the stock ( which is 100) to deduct the number typed in the quantity coloum
however to stay as that new number even when the number in the quantity
coloum is deleted because then when i type a new number in the quantity
coloum it will deduct that also which makes the stock control system

 

[Guest]

easiest thing I can think of is to set up a macro.
Record a macro where you type in a helper column:
=(field with stock number-field with quantity number)
copy this column, paste-special/values into the stock number column.
Delete the helper column.
stop recording
Add a button to your sheet using the drawing toolbar
Right-click the button and select Add Macro...
Add the macro you just made
When you're ready to update your stock column, click the button...