I'm not sure wether I've got the question right:
every Pronto-shutter looks like yours. It has got the 25, 50, 100, 200 (/250
nevertheless they're never really faster than 1/200
) markings and these are the distinct steps to which it can be set.
The selectable shutter-speeds vary only between the different types of shutters made by AGC. The Pronto is pretty much the "very basic version" of the Prontor, which has an extra set of drives to it where yours has some empty space on the top right of the casing. (Hope I remember the position correctly.)
There is no variability in shutter speed between two settings. It is either (e.g.) 50 or 100; never sth. like 1/80.
Hope that answers your question