Felt S32 Wheel Size

Q1.  I have a 2008 Felt S32 with stock wheels/tires (700x 23cc).  I'm trying to determine the circumference so that I can program my bike computer.  I'm not good with measuring.  I've come up with a couple of different numbers.   Does anyone here know the true circumference that that tire ?

Q2.  I could use the chart that was provided by the bike computer to guestimate the circumference but the numbers wouldn't be as accurate as a true measurement.  Does this really matter ?  How much difference is it in reality if I use the guestimated version versus a true measurement ?

Thanks.