The strength of a signal on the tvfool report is given in two ways.
The first way shown is the Noise Margin, or NM for short. The TVFOOL FAQ says that a signal must have a NM of at least zero to be received, but you can add the antenna gain to make the NM more positive.
Both of the NMs are negative, so the -10.0 dB signal is weaker.
FAQs here:
http://www.tvfool.com/index.php?opti...ask=view&id=57
The signal Power in dBm is another way to state the strength of a signal, and can be measured with a signal level meter. Most tuners require a signal to be at least -85 dBm, but you can also add the antenna gain and the preamp gain to make it more positive (less negative) if it is weaker than -85 dBm on your report.