Inventory management how to deduct stock from sheet 1 and amend stock value on sheet two

I am really struggling with a formula for the following situation.
I am trying to create a Job report on sheet 1 called "service order" On this service order i have created a table with the following information,
Column 1 is (drop down)part type,column 2 is dependent on part type(column 1) and is part description again drop down, column 3 is part number drop down dependent on previous selection. Column 4 is unit type and auto fills on column 1 selection. Now Column 5 is the quantity used.
So on sheet 2 i have called "stock list" which has the stock amount for each item.
What i want to do is if i use a part on sheet 1 (service order) i want to deduct the amount used for that part on sheet two.
My difficulty is that the items on sheet 1 are dynamic with the drop down boxes.
I am fairly new at excel so any help would be great.tks.

Hi and welcome
Attach a sample workbook (not a picture or pasted copy). Make sure there is just enough data to demonstrate your need. Include a BEFORE sheet and an AFTER sheet in the workbook if needed to show the process you're trying to complete or automate. Make sure your desired results are shown, mock them up manually if necessary.

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Hi all,
I will try to rephrase what i am trying to do. I have two sheets. Sheet1 = service order, sheet 2 = stock list.
If Sheet1(service order) Cell 1A = any cell in Sheet2 (stock list) Column A, then deduct entered value in cell E1 (sheet1) from value in column G(sheet2) for that part and enter value into current stock (sheet 2)Column H for that selected part.
So recap cell 1A on sheet 1 is "part description" this is selected from a drop down if that matches a cell in Column A (also part description list) on sheet 2 then the value (amount used) entered for that item in cell E1 sheet1 is deducted from the issued amount in Column G (sheet 2) and the value is updated for that item in the corresponding cell in H.

Formula is probably something like this, IF 1A(sheet1)=ColumnA(sheet2) then ColumnG (sheet2)- E1(sheet1)= value column H sheet2

Hi Alan,

My apologies, i have posted this question on one other site. I can try and take it down. I am only new on both forums, so it is a genuine mistake. What can i do to rectify this. The last thing i want to do is waste anybody's time.

Thank you Alan for your understanding. If i get a resolution i will make sure i inform both sites. I have since read the house rules on both forums so i am
more familiar now with the rules. This is probably something i should have done at the beginning. Again thank you for your understanding.

Hi Alan,
I pm'd you can you take this thread down for me please? I don't think my PM is working. I want to raise this in the commercial services.