That difference, 2135/2096, is just a 1.8% difference. (but 1.8% at 50 miles is 0.9 miles.)

I always do the rollout method. Sight downwards by the front hub to the tire valve. I try to put some weight on the bike as I roll. I use a couple of pieces of tape, aligning the valve to the first one, then sticking the second after one revolution (or even after two revolutions, and divide by 2).