What is the name of the tool?

VU meters are a guess at best. Watts are frequency dependent and the real measurement includes the frequency and distortion levels, This requires expensive testing equipment. I have had amps with and without power meters and to tell you the truth, you don't need them. They are just cool to look at but they don't add one bit of useful information. When you clip your amp, you'll know it. If you have a high power unit, you'll break your loudspeakers first before the amp gives up. Plus it's not a good gauge to judge if you are near the limit, your ears or your loudspeaker fuses will catch it before your meters tell you anything. 

I have had amps with and without power meters and to tell you the truth, you don't need them.

Blasphemy!!

Thank you guys very much for you answers while not being arrogant. This is why a newbee like me wants to stick around.

I love meters. Mcintosh makes their own meters and takes pride in their accuracy. I’ve learned a lot from them, especially how little power is needed to make a decent amount of noise. Save up for them,their worth the extra money.

"...Mcintosh makes their own meters and takes pride in their accuracy..."
I just sold my Big Mac amp with those gorgeous power meters. But my Parasound A21 (or the JC1s for that matter) don't have any meters and they sound better to me. 
 

"... especially how little power is needed to make a decent amount of noise..."
So you are using the power meters to see how little power you are using? 1 watt goes a long way.....