25 Tikka,
I have a 3-9x 36 Dia-vari C that is marked "Made in the USA", so apparantly there are different versions. It blows my 3-9x 40 Conquest away optically. The adjustments on mine are marked 1/4" on the elevation and 1 cm@ 100 meters on the windage adjustments.(American or German workmanship?) When I squared a box with it (20 click) to check that out I ended up with perfectly spaced groups 5 inches apart with a final 3/4" 6 shot group at the starting/ending point. Not bad, considering I did it with a .375 H&H. Turns out it is 1/4" BTW.
As far as I know, the Conquest replaced the American made Diavari "C". If thats what you have, they don't make them anymore.