I'm a freelance editor and this graph is in a report and labeled as a log scale. (The version you see is my revision that removes the words "log scale".) The client insists that it is a log scale, it doesn't seem like that to me but then, I'm an editor and afraid of maths. If it makes any difference, the two quantities are indexed to each other where 2011 = 100.
It is not a log scale.
Every time you go a certain distance upward, you add $20$.
On a log scale, every time you go a certain distance upward, you multiply by a particular number.
When you go from $100$ to $200$, you multiply by $2$. When you go that same distance upward again, you'd multiply by $2$ again, getting $400$. Then the same distance again and you'd get $800$, then the same distance again and get $1600$, and so on.
In this graph showing bitcoin prices as a function of time, every time you go from one of the horizontal lines up to the next, you multiply by $10$.