My Strada Cadence cyclocomputer odo is about 2-3% off. I know it's not a big difference, but i would like it to be dead on accurate. I just changed tires the other day and it was dead on before i changed. I have it set for a 700x35c tire, which are the new tires. I'm going farther than what the computer is saying. I know that i could change the tire setting, but how do i make it more accurate? Would i set it for a bigger tire or smaller tire?

You need to measure the actual distance your wheel travels in one revolution and load that value into your computer. That is the only really way to be really accurate.

First off, are you sure you have the tire size set right? This computer has the ability to have 2 tire settings, which are each notated by a little A or B icon on the screen. Before you go messing around with new settings, try to make sure these are correct for your tire size. A 700x35c should have a setting of 2168.

If all that checks out, you should make the setting smaller. Maybe try a 2162 or even a 2160 and see if that is better.

What are schools teaching in basic math skills these days?

If your mileage readings are high; e.g., you get 103 miles on a 100 mile course, apply a correction multiplier equal to (100/103) to the nominal setting for your tire. Conversely if it's reading low; e.g., you get 97 miles on a 100 mile course, apply a correction multiplier equal to (100/97) to the nominal setting for your tire. In both instances, of course, you have to round to the nearest integer value, as your bike computer will only accept whole numbers.

If it's reading 2% low, then increase the setting by 2% (multiply whatever it is by 1.02). Not real hard. Remember, it's just counting revolutions, and every time it counts one, it "gives you credit" for having rolled forward whatever it has been told the circumference of your tire is. If it's reading low, that means the tire is bigger than it thinks it is and you should increase the setting. If high, then it thinks the tire is bigger than it really is and you need to reduce the setting.

I don't think that rolling it out is all that accurate, I use it as a starting point, but then I put a hiking GPS on my bike and ride 20 miles or so and reset it to be accurate to that.

Sheldon Brown's site details the measured course and correction by a percent method as suggested above. I go directly to this method. Use Google Maps or Mapquest etc. to measure out a course of a few miles, preferably as straight as possible. Ride it and correct the cyclocomputer accordingly.