How to calculate the average wage increase? What is the average wage increase and how does one calculate it? Gottfries (2013, p. 166) refers to the following formula as the "average wage increase:"

$$\frac{\Delta W_t}{W_{t-1}}$$

If the above formula is meaningful, then my question is more a clarification about terminology and notation. 

As to terminology, what is a more popular way to refer to this equation other than the average wage increase?

As to notation, Gottfries refers to $W$ as the "average wage level," but what do the other symbols mean? Is it safe to assume the expressions $W_t$ and $W_{t-1}$ refer, respectively, to the average wage levels at times $t$ and $t-1$? What then does $\Delta W_t$ represent? Is $\Delta W_t$ the difference in average wage levels at times $t$ and $t-1$ (i.e., $\Delta W_t = W_t - W_{t-1}$)? 

I think this question is worth asking since 1) there has to be a more popular way to refer to this equation (Gottfries book was all that came up when I Googled "average wage increase") and 2) I don't want to assume, as far as notation goes, more than I have to (Gottfries doesn't define these symbols).
This is a very standard % change over time formula.

It is simply:
Change Between Years / Original Value

$ΔW_t$ means the change in wage from year $t-1$ to year $t$ (where $t$ represents an arbitrary amount of time). You can easily calculate that by: $ΔW_t=W_t−W_{t−1}$.

Thus it is simply saying % change over time is $\frac{New - Old}{Old}$.

Middle school math with more symbols.