Monthly cost calculation of bitumen 60/70 and 80/100 in Iran

Bitumen price updating monthly in Iran and cost claculation of bitumen 60/70 and bitumen 80/100 has formalu which is control and reporting by NIORDC (National Iranian oil refining and distribution company) by end of each months(local calender) which is 22 of each Christian calender.
If:1.63<K/F<1.73
Then bitumen price will come up based on FOB of BND and 10% as cost of transport and process will deduct then put in IME to do the deal. This formula adjusted 10 years before and still there is scale for cost calculation of bitumen on ech month