Pain should not defer someone from getting a tattoo, yet it does not mean we do not get curious about the pain we will be putting ourselves through when we undergo the needle. However, all pain charts seem to vary.
I wish to compare what I know. I have a thigh tattoo and a sternum/ under-boob tattoo. For thigh tattoos Each chart tells a different story for the pain you may be in store for with thigh tattoos. For sternum only one chart shows truly one sternum spot, and list it as a very painful spot (and I agree).
The reasons for these variances is human experience. Humans all experience pain differently, and handle it differently. So each location can be handled very differently depending on the person. Most people know how well they handle pain, and these basic pain charts can give the concept of what to expect in my opinion.