Constructional stretch
 

I checked the NE Ropes site and cannot find a listing for the constructional stretch for Endura 12 now called I believe HTS 75. I've used it before but not where the finished length is critical. Any help? BTW I will be using 3mm line with an eye splice in each end.

Stretch
 

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