What is meaning of negative dbm in signal strength?
When we try to get nearby cells and their LAC, MNC, signal (and while using other android apps) we are getting signal as negative value (like -85dbm). How should I take this? Should I ignore -ve sign and take absolute value or -85 is smaller strength than -60?
How this will affect my location finding?
Answer
The power in dBm is the 10 times the logarithm of the ratio of actual Power/1 milliWatt.
dBm stands for "decibel milliwatts". It is a convenient way to measure power. The exact formula is
P(dBm) = 10 · log10( P(W) / 1mW )
where
P(dBm) = Power expressed in dBm P(W) = the absolute power measured in Watts mW = milliWatts log10 = log to base 10
From this formula, the power in dBm of 1 Watt is 30 dBm. Because the calculation is logarithmic, every increase of 3dBm is approximately equivalent to doubling the actual power of a signal.
There is a conversion calculator and a comparison table here. There is also a comparison table on the Wikipedia english page, but the value it gives for mobile networks is a bit off.
Your actual question was "does the - sign count?"
The answer is yes, it does.
-85 dBm is less powerful (smaller) than -60 dBm. To understand this, you need to look at negative numbers. Alternatively, think about your bank account. If you owe the bank 85 dollars/rands/euros/rupees (-85), you're poorer than if you only owe them 65 (-65), i.e. -85 is smaller than -65. Also, in temperature measurements, -85 is colder than -65 degrees.
Signal strengths for mobile networks are always negative dBm values, because the transmitted network is not strong enough to give positive dBm values.
How will this affect your location finding? I have no idea, because I don't know what technology you are using to estimate the location. The values you quoted correspond roughly to a 5 bar network in GSM, UMTS or LTE, so you shouldn't have be having any problems due to network strength.