It would appear that the Calculator for XM819 rims doesnt cater for the Nipple Eyelets – I tried building on pro 2 with 260mm spokes – but they are way too long.

Can anyone clarify the spoke lenght required?

The DT Swiss calc worked for me with XM819 rims; Mavic do suggest using 16mm nipples with their UST rims – I used them in my build and I think it would asist in lacing, over 12mm nipples.

cheers, can you remember what lenght spokes you used?

That’ll depend on the hubs you used – mine were DT Swiss 440’s front and rear, three-cross with 16mm nipples: 256mm rear (both sides) and 255mm left, 257mm right at the front. First, and so far only, wheelset I’ve built and they’re still fine after a year and a half!