I've not used DT so can't comment on those. Couple of hopefully- useful links:
Stumbled across this, which has ERD figure in it for Alesa Xplorer 26". It appears the same as the 700c figure in the same table. One must be wrong.
https://jmoore.me/wheelbuilder/rims/list/3?search=&forr=
And in case you want to double check (advisable!)
https://www.parktool.com/blog/calvins-corner/measuring-effective-rim-diameter
Yes great idea. I will see how they work out.Measure in 3 places round the rim....add up and divide by 3. That way if the rims a bit oval or you were a little inaccurate, it will all compensate.