Dan's suggestion (in the book) is to visually compare between the test print and the screen display. Size both the step wedge and the print to be the same size and do a side by side comparison.
Me, I'm a little bit more obsessive than that. Besides, I think that a visual comparison at either the low or high end of the step wedge requires "a really good eye" for tonal comparison.
I sprung for the reflection densitometer because I am committed to the digital negative process.