Posting Reply got from Mod sir in pvt, to let others also know this query.
"
PNR Accuracy = No. of Correct Predictions/Total Predictions. Cancelled tickets don't count.
PNR Predictions are separated into 3 slabs:
Current...
more...

(< 30 days),
Recent (30 - 60 days) and
Old (> 60 days) predictions.
Each of the 3 slabs have their independent PNR Accuracies calculated using the simple formula shown above.
To get the Aggregate accuracy, we average out all 3 of the above numbers, but provide different weightages.
Recent Predictions get twice the weight of Old Predictions.
Current Predictions get twice the weight of Recent Predictions.
.
We have done this because people's PNR Accuracy usually improves with time, as they get more experience, and we do not want their old bad predictions to reduce their overall accuracy %.
.
Example:
Say you have made 200 total predictions out of which 100 were correct.
100 Tot Predictions/60 correct were made before 60 days - OLD
70 Tot Predictions/30 correct within 30-60 days - RECENT
30 Tot Predictions/10 correct within 30 days - CURRENT
Your accuracy % is:
(60*1 + 30*2 + 10*4)/(100*1 + 70*2 + 30*4) = 44%
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In the example, you have made 50% total correct predictions 100/200. But in the past 30 days, you only got 10/30 correct. Since we give more weight to current predictions, your overall accuracy is only 44%."