Most potentiometers will not list on the body of the pot if it is Linear or Logarithmic and it is often a question that is hard to answer for our customers. If the pot they have is still functioning you can often tell which you have by doing a simple resistance test on the potentiometer. Below I done a test on two similar 10K pots from TT Electronics to help demonstrate the differences.
First I have a Linear part P160KNP-0EC15B10K. In the first picture I have the shaft turned completely to the left and you can see I am almost to 0. The second picture I have the shaft turned to the mid-point and you can see I am at approx 5K. Then the last picture I am turned completely to the right and I am at 10K.
Now lets look at part P160KNP-0EC15A10K which is a Logarithmic pot. Again I turn the shaft completely to the left and I am at almost 0. I then turn the shaft to the mid point and this is where I see the difference. At the midpoint you see I am only at 1.67K. (Depending on the curve you may also see a high number in the middle). Last I turn all the way to the right and again I am at 10K.
Here is a Chart that Bourns offers with their PDB241-GTR Series of Pots. As you can see the A2 and C2 tapers would be Logarithmic and The B0 would be a linear taper.
