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Which and how much mathematical operations are required for the blockheader-to-blockhash operation and how fast would a human be able to calculate a single hash?
EDIT: For simplicity, I think it's a good idea to use the world record for mathematical calculations to make it a little more fair.
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The user C121 on r/bitcoin explored this topic in the thread Mining Bitcoin by hand.
He states that it takes 3385 integer operations to calculate one double SHA-256 hash.
His conclusion was that you would reach about 0.00003 H/s, or in other terms, it would take about 9.4 hours for one hash, assuming the human in question could do a 32-bit operation in 10 seconds.
He also estimates that you would fill about seventy pages of paper with the calculations per hash.
Update:
As Mathias711 pointed out in the comments, Ken Shirriff actually calculated some SHA-256 operations manually and wrote an article about mining bitcoin with pencil and paper. He arrives at an estimate of 0.67 hashes per day, at a vastly uncompetitive energy consumption. ;)
Hmm, with a bit of pre-made tools (mechanical or not), we can actually steeply reduce this number right? – Pacerier – 2014-05-22T16:55:02.703
5Do ASICs qualify as 'tools'? – Pieter Wuille – 2014-07-05T11:01:34.810
This guy actually did it, and he reached 0.67 hashes / day. – Mathias711 – 2014-09-29T10:48:01.913
I was actually just about to link this myself. I'm sure with practice you'd increase the number but humans make mistakes after hashing for long periods of time, I'm sure. – Wizard Of Ozzie – 2014-10-01T06:30:57.807
2I think that would depend a lot on the which human... – Eric Petroelje – 2014-01-23T21:54:18.867
@Steven, It's a better idea actually to use the average person than world record holders.... – Pacerier – 2014-05-22T16:53:46.177
@Pacerier Well, it's hard to get records of the average human's performance in big calculations than to get the world records holder because his performance can probably be found in record books. – Steven Roose – 2014-05-24T21:09:42.700