I find my Nuarc to vary with the ambient temperature. 10C = fast exposure, high contrast underexposed, 15C = normal, 20C = very slow, low contrast and over exposed. So to get reasonable results I have to use different dichromate percentages and slightly alter exposure according to temperature. Took a while to work out.
I adjusted the spiral thing on the integrator to allow the max light to enter in an attempt to even out its inconsitencies but that made no difference except to how fast it counts. The perspex cover on the integrator has cracks from time and exposure to UV so I have considered removing it or replacing it with something else.