apply formula if number is the last repeat

Guys Greetings for the day.

I'm looking for a formula to be used on the attached workbook in the "S" column that can apply the given formula "=IF(Q4=0,0,L4+Q4-M4)-R4" only if the item code on "H" column is the last repeat of the sequence.

because I need to highlight the variance quantity on the "S" row referring to the "H" column items number just for each unique item code and the repeated numbers will return empty results.

I have attached the screenshot example as well as the workbook for reference.

DSMR Report.xlsm

232237253723587.jpg

@Glenn Kennedy this is for sure brilliant, it's an amazing result bro.

thank you so much and keep safe brother

i did already thank you brother much appreciated

Originally Posted by HansDouwe

You didn't say anything about my solution in Post #4 (posted at the same time as your post #3)

@HansDouwe thank you so much for offering the solution I really appreciate that as well. but the solution of @Glenn Kennedy is much more suitable because of the filtering that I might be doing on the data and that was taken into consideration thankfully.