"The elegance of the Kirana sale/checkout is efficiency - no barcodes to scan, no POS to deal with, and it's probably 3-4x faster than any modern checkout process. However, there is one tool they always use - a calculator."

As someone that has worked a cash register both with barcodes and scanning, and doing the same thing with a calculator when power/computers crashed, I don't know how you can say a calculator is more efficient than a proper POS.

Labour efficient? Time efficient? Tax avoidance efficient?