If you are interested in knowing about UPSC's mains answer- sheets evolution process, you can read this open-secret PDF-submission by UPSC in SC. It is old but still relevant
Moderation เคเฅ เคฎเคพเคฏเคพ/ Inter-subject moderation in optionals- It is a complex process that can vary from year to year across subjects and papers - เคเคธเคชเคฐ เคเคฐเฅเคเคพ เคซเคฟเคฐ เคเคญเฅ......