How to see if your PH meter is accurate?

Hello all i just bought a cheapo digital ph meter on ebay and in the manual it says it comes pre-calibrated. How do i check to see if my ph meter is accurate without buying anything? Anyone have any ideas or input??
Thanks

Don't know how you could be 100% positive without buying some calibration solution. I don't know if distilled water is always a level PH or not.

white vinegar might be a pretty precise known ph, or you could buy some test solution

You can check it with distilled water. It is always 7.0. Put it in distilled water for awhile and then adjust to read 7.0. BUT, the electrodes should be stored in a good storage solution and the calibration solution doubles as that. You would be better with some 7.01 calibration solution, it will last a long time.

test solution. Its like 1 dollar for a little packet I think.

Just put some lime juice in a cup of water from the faucet (where I live faucet water is at little over 7 ph), as you add lime/lemon juice to a cup of water it should start to become more an more acidic as you add more lime/lemon juice. This method is prob not that accurate but if your meter senses the acid from the lime/lemon juice chances are its not precise but close enough.