Two ways to check tension, by sound or with a Park TM1 tensionmeter. The sound method simply involves tapping with your fingernail a couple of spokes you know were good, then go to the loose ones and do the same, then simply adjust the spoke tighter if the sound is dull or low or looser if the sound is higher. The tool cost about 57 dollars. Is the tool worth it? If your building wheels for a living yes, but otherwise no. I never had that tool, in fact don't even own a truing tool, and haven't had the need in over 40 years of messin with bikes. I simply use the brake calipers to true the wheels by closing down the calipers till they just barely miss the rim, then spin the wheel till a caliper hits the rim then adjust accordingly. Tension wise I just hit the spoke with my finger nail and listen for the sound, and you can tell by spoke movement where two spokes cross. See this for more detail:
http://www.bikexprt.com/bicycle/tension.htm
And this for truing:
http://www.ehow.com/how_5036725_true...ing-stand.html