"Impact on revenue can only be assessed after coal sampling and analysis over a reasonable period of time," CIL said informing the bourses.
As most of the coal was dispatched to power sector, ultimate realisation from sale was derived from analysed grade done through third party sampling assessment system prevalent since October 2013, it said.
A total 871 samples from 386 mines were drawn by the academic institutions as per Coal Controller Organisation prescribed methodology and based on their report, final coal gradation for 2017-18 were announced.
Coal India said 40.76 per cent of the samples drawn were downgraded, while only 7.67 per cent got upgraded and 51.5 per cent faced retention of quality.
Gradation of coal is an annual event by the Coal Controller.
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