Edit: .005 is for the old brass 510's
Almost every vt200 mod resistance has been .005 but john said to use 80% of that value and use that as the mid resistance. I'd just set it to .0045 and call it a day. I actually set mine to .0048 . you can test your own by having the mod resistance at 0 then threading a copper bolt into the 510 or even shorting out the 510 with just thick wire touching both pin and threads. And look at the resistance the atty analyzer is giving.