so what are you using for pi? if you are using 3.1415 then the diff between 1.77 and 1.78 would be at least more understanding. but if you are using 3.14, then you have already added error to your equation. you already have a .001 plus or minus rounding error.
so in everyone's best interest and not to induce errors in rollout calculation we should all be using 32/18 for internal and circumference divided by diameter for pi. we don't want to miss that 1 * 10^-1005 now do we?