Cluin: "During a discussion among the club's membership board at St. Andrews in 1858, one of the members pointed out that it takes exactly 18 shots to polish off a fifth of Scotch. By limiting himself to only one shot of Scotch per hole, the Scot figured a round of golf was finished when the Scotch ran out."
Clearly an urban myth. the "Fifth bottle" is an American standard. The standard bottle in the UK was (until late in the 1900s) 1pint 6 2/3 fluid oz. With a standard English measure being "one sixth of a gill" i.e. one twenty-fourth of a pint. By this it can be seen that there were 32 standard measures (or 16 'doubles') in a full size standard bottle.
At the same time the standard Scottish measure was slightly larger at "one fifth of a gill" i.e one twentieth of a pint. Meaning a 'bottle' was never quite properly finished.

Modern bottle sizes have been 'Metricated' as 1 litre or the smaller 75cl. But measures have become larger at 25ml, making 40 full measures to a litre bottle, or 28 measures to the smaller

Nigel