Constructional stretch

[Brion Toss]

Hi,
A foot in fifty feet (2%) is a good rule of thumb for most HM ropes, but where finished length is critical, one needs to impose a load that removes all constructional stretch, and mark the line while the load is on. This is what we do for Dux standing rigging, so you might want to check out Colligo's primer on the subject. Take-up from the splices is also an important part of the calculations.
Fair leads,
Brion Toss