You appear to have answered your own question....
Calendar rate gives you the "annualised" rate taking into account stoppages, reduced flow, shutdowns etc so that the accountants can work out the yearly numbers using a lower number.
Oil or daily rate gives the volume in one day or hour or whatever you've divided by and is used to size equipment.
the first on a good system is probably 95-99% of the second one.
On a poor system it might be 80% or lower.
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Also: If you get a response it's polite to respond to it.