The signal meter on many, if not most TVs reflects the digital error rate, not the signal power received. So, an amplifier may well be increasing the power level, but the reported signal 'strength' appears unchanged because the error rate has changed very little.
The least expensive option I have found for a meter that indicates power level, pre-forward-error-correction error rate and post-FEC error rate is the SiliconDust HDHR type tuner.
http://forum.tvfool.com/showthread.php?t=820 While it is not calibrated to a standard unit scale, the information displayed is very helpful when judging antenna aim and assessing signal level vs. quality.
Please keep in mind, an amplifier is going to amplify desired signal and received noise equally. So an amplifier is not going to 'pull' more signal from the antenna or air. An amplifier can only 'push' a stronger copy of the signal and noise that is connected to the input down the line. An amplifier's job is to overcome losses in cable and splitters connected to the output of the amplifier. To get the most benefit from an amplifier, it should be located close to the antenna, before the signal is reduced by cable loss.
If you need to boost the quality of a signal, start at the antenna and it's mounting location. An amplifier is not a substitute for the correct antenna mounted in the correct location and aimed the right direction.