I will add my 2 cents. Ask your string maker what he prefers. I ask my customers to measure their current string, off the bow, end to end. This give me the most accurate measurement to build their new string by.
Going from a dacron string to a FF string, or vice versa, can require some adjustments.
I recently had a customer give me a measurement. I built his string accordingly. When he got it, he called to say it was WAY too short. He then told me that the measurement that he originally gave me was from the bottom of the "V" on each loop. This caused the string to be over an inch too short.
Simply communicating with your string builder if your aren't sure will go a long way.