"A vaper without a multimeter is like a doctor without a stethoscope."
-Switched
Buy a multimeter. Any digital multimeter will do, you don't need a Fluke! You can get a good one for $15-25 from Sears, Lowe's or on the Amazon. You need your multimeter to check the resistance of your atomizers and/or voltage of your battery.
Connect the black test lead to the jack marked "Common" or "-"; connect the red test lead to the jack marked with the Ω (Ohm symbol) or letter "R" near it.
To check the resistance of your atomizers:
1. Turn your multimeter on and select the lowest Ohms setting, usually 200Ω.
2. Look at the display; the left side of the screen should display number 1.
3. First, test the resistance of your leads. Touch to two leads together, firmly, and wait for numbers to stabilize. On the right side of the screen, you should see a number between 0.0 and 0.4, or so. This is the resistance of your leads. Remember that number.
4. Now, to test your atty. Position your carto firmly on your desk; you don't want it to slip and slide all over the place. Touch one lead to the hole in the center of the atty and the other lead to the threads. Again read the display after the numbers have stabilized.
5. Subtract the resistance of your leads (#3) from the resistance of your atty(#4). This is the resistance of your atomizer.
This process takes some getting used to. Steady hand helps. Just keep practicing and you'll figure it out.
There are many tutorials on Youtube--watch them if you're a visual learner:
I like this one by GeekGirlVaper:
If you only want to check the resistance of your atomizers (or are going to build your own coils), you may want to consider buying this Atomizer and Cartomizer Ohm Meter--a very nifty, albeit single use, device: