Granite by area, piece and weight
Stone here is quoted by the square foot for slabs, by the piece for cut sizes and by weight for blocks, with a wastage allowance on top. Holding the unit and conversion against each item removes the arithmetic, and showing wastage as its own line rather than folding it into a rate settles the argument before it starts.
Irrigation and project work
Large irrigation and infrastructure projects bring contractors working to formal terms with purchase orders and audited payments. A referenced invoice with HSN codes and line-wise tax, plus a challan naming the vehicle and receiver, are what get bills cleared rather than queried.
Lot matching for a returning buyer
Granite from different lots does not match, and a customer returning weeks later expects the same shade. Keeping each lot as its own item with its own rate and stock answers that without walking the yard, and it prevents a premium lot being billed at an ordinary lot's rate.
Credit across project and farm buyers
A project contractor waiting on a government process and a farmer settling after the harvest are both slow for different reasons. Ageing rather than a total shows which is which, and a limit per party keeps either from growing past what you can carry.