Hey bobby I took an updated pic for you. It was of the original design, but I did mix some of the new pieces at the top. I was wrong it was a 6 gallon carboy. The LHBS store sells both 6.5 and 6, I got a 6. I can snap one real quick if you want of the new design.
Bobby, if you aren't comitted to a final design yet I have a couple of suggestions.
I personally like the un-numbered small graduation marks like the above with a medium size indicating 1/2 and a small one for 1/4. If you use the triangles like the above you could probably get your cutter to do the 1/2s and 1/4 in between the full numbered graduations. That way you could easily do 1/2s and 1/4s for every gallon with no extra material, only a little more hand picking time on your part. You could also offer the un-numbered 1/2 and 1/4 graduations separately if you want. Personally I'd go with a full set, but others may only care about 1/2s and 1/4s up near the 5gal mark and up the neck where the graduations vary because of the taper.
I'm glad you're testing the numbers out with different cleaning chemicals, water temps and sanitizers. I think PBW, Oxyclean, Bleach, TSP, StarSan and Iodophor along with hot water would cover 90% of the cases.
One other thought, the one that made me open and read this thread in the first place. First though, I love the graduations for the car boys, especially the white. However, I just went through the exercise of filling and remarking all my white plastic primary and bottling buckets for a 3rd time. I've got a couple of different capacity and diameter buckets and I just find all the factory markings way off and totally unreliable, sometimes upto 1/2 gal off. I used black Sharpy marker to recalibrate the graduations on them and, although I can mark them clearly by hand, the Sharpy washes off after a 5-6 cleanings. So my thought is this, offer the graduations in both black for buckets and white for carboys.
I'll buy a half dozen of each.