Analyze g Histogram of Y values (shift-F6)

You have to specify the number of bands (default 10) and the Y-range within which the Y values will be counted. 

 

Histogram of 10 bands, with a Y-range from 0 to 150

If the number of bands specified is very high, the resolution is very high as well, but the number of values in one band will be very low. You can fix this by downsampling in the way below:

Analyze g Downsample (average X, add Y) (ctrl-shift-F6)

Especially made for histogram purposes. Normally, downsampling takes the average of the X values as well as the average of the Y values. In this case however, it takes the average of the X values and adds the Y values. This way you can combine several histogram bands into one.