Would you believe I found this on the .net whilst looking for something else. It explains the two measurements!
"As the story goes, Easton changed to the 28" and 1.94# weight because an employee in the plant several years a go decided he should check the weight they were using on their spine tester which was 26" centers and found the weight to be 1.94# instead of 2#, (in the real world that .06# difference really didn't make enough difference to worry about). This presumedly caused panic within the ranks and a new system was suggested to ATA, of which Jim Easton was President at the time. In those days most everything was compound so the change really had no adverse effect, as the strike plate depth is easly changed on a wheel or cam bow. The problem started when Trad archery had its resurgence. The new standard just doesn't work for a trad bow. If I were shooting carbon arrows I would spine them on the old system, spine is spine and the old system will work with any shaft material. The only problem will be the lack of different spines in the carbon world, so you will still have to play with arrow length and point weight, but it will give you a starting point closer to what you need. Have you noticed how few aluminum spines are now available today as opposed to 20 years ago, that has made it much more cost effective to Easton. Folks its all about dollars in their pocket, not about whats best for the archer or archery."