I could be wrong, but I thought it was that a cartos ohm will slightly drop, not rise, after continued use and buildup.
Most cartos will be +/- .2 ohms. Thats why when you
buy cartos, alot of the boxes that they come in will say that. I use the Ressurector cartos, which are 1.7ohm, but on the box they come in they say 1.7ohm(+/-.2ohm) So just bc a carto says a stated ohm, doesnt mean that it actually is always at that exact ohm. Some crappy cartos Ive even seen say +/- .4ohms, which is a big variance, but most are +/- .2ohms. The Ressurectors are one of the most consistant cartos Ive found though and they almost aways meter dead on at 1.7ohm.
Are yo using a digital multimeter to test them? I dont know if I didnt read it right, but I dont understand what your doing to test the ohm. What do you mean you subtract 1 from the number, do you mean 1.0ohm or .1ohm?
Not all multimeters are exactly the same.
To test the ohms you want to touch the red to the center pin and the black to the outside
threading of the carto. Hold it steady until the reading steadys out and you get a consistant number without it jumping around. Remeber that number. Then you want to touch the Red and Black pins together and that number is what you subtract from the ohm you got for the carto. You have to make sure you touch them together and hold it very still until it stops jumping around and you get a steady reading.
With my multimeter when I test a Ressurector they come up at 2.6ohm, and occassionally 2.7ohm. Then when I touch the red and black together I normally get 0.9 and occassionally 1.0. When I get 2.6ohm on the cartos, the red and black pins together are normally 0.9, and when I get 2.7ohm on the carto, the red and black together are normally 1.0.
Either way 2.6ohm-0.9ohm=1.7ohm and 2.7ohm-1.0ohm=1.7ohm, which is what they should read at.
But occassionally like I said, they can be +/- .2ohms so sometimes one of my Ressurectors will read 1.8ohm or 1.6ohm. I havent had one yet be more than .1ohm off what it should be, but its def possible and fairly common in cartos.
I dont know if thats what your doing to test the ohms, and if it is, sorry I didnt pick up how you explained it