Power Testery Thingy-ma-bob

[tesco]

hey guys, my grandma had an electrician at her house trying to fix the power for her stove and left behind a power checking thingy. we tried calling him but he never came back to get it so today she gave it to me. ive been playing around with it just checking voltages of stuff on my computer but i want to know more about this thing.

1. What is the real name for these power checkers?
2. What else can i use it for?
3. Where can i find a manual for it? it is an Escort EDM168A.
4. What are these things worth? i am assuming they are a lot.
5. Can somebody tell me what all of the different settings on the dial are for?the dial spins both ways and it has about 25 different positions.
5. there are 4 jacks at the bottom of the checker that i can plug in the red and black wires too. they are labelled:
a. 20A
b. mA
c. COM
d. V-[ohm sign]-Hz
What are each of these for?

im currently using it in DC mode, the dial is set to 20 in the V (volt) section, and the wires are plugged into c and d.

it seems to work like this for DC voltages but im afraid to use it for AC
6. How do i set it up for use on AC ???

thanks a lot guys if someone can answer these questions (especially the manual one) it would be greatly appreciated thanks!

[lynx]

1. They are called multimeters.

2.
EDM-168A 

2,000 Count Display Resolution
DCV, ACV, DCA, ACA, OHM, Diode, Audible Continuity
  Frequency,and Capacitance Measurement Functions
0.5% Basic DCV Accuracy
DCV Measurement Range from 200mV to 1000V with 100μV
  best Resolution
ACV Measurement Range from 200mV to 750V with 100μV
  best Resolution
Average AC Measurement, ACV and ACA 40-400Hz
  Bandwidth
DCA and ACA Range from 200μA to 20A with 0.1μA Best
  Resolution
Resistance Measurement Range from 200W to 20MW with 0.1W Best Resolution
Frequency Measurement Range from 2kHz to 200kHz with 1Hz Best Resolution
Capacitance Measurement Range from 2nF to 20μF with 1pF Best Resolution
hFE Measurement Capability 
Manual Ranging 
Reverse Polarity Indication 
Low Battery Indication 
Overload Protection 
Fused Protection for mA and 20A Input 
Input Warning for Wrong Input Connection

3. I've no idea where you would get a manual, but they are largely self explanatory.

4. That one doesn't look particularly special, but it does have overload protection. Probably cost in the region of $75-100 new at a guess.

5. The dial selects what you are measuring, it has to match the sockets you are using.

To measure current up to 20 Amps use sockets a and c.
To measure very small currents (milliamps) use sockets b and c.
To measure AC volts, DC volts, resistance or frequency use sockets c and d.

The overload protection should protect it if you get the dial/sockets wrong.

6. See above

I've seen two different pictures of this multimeter. One had a dial with lots of positions, the other had fewer positions on the dial but had buttons above. I would guess that on the second one the dial selects the type of reading and the buttons select the range etc.