You can also turn on the "Show Density" function and use it as a basic densiometer.

For the record, the Epson application does the same thing: as you mouse over any region, you see the RGB values below. It's a feature that is always on,as far as I know.

What the Epson L value shows, is not the raw input value detected by the scanner (which is what a densitometer would reveal), but rather the output value you will get in your file, after performing scanner adjustments. This way you can set the low-end of the levels or curve, so that the clear film edge is clipped to a luminance value of 0, but no more.

This is a "digital equivalent" of giving the minimal print time required to render the film edge as Zone 0.