My thinking being 2 crank revolutions between the markers should equal twice the actual RPM, not half.

EDIT: I figured out my mistake. I knew I was measuring two revolutions  of the crank and didn't take into account that the software measures what ever is "between the markers" as a "single" revolution in it's calculation.

I was thinking double the revolutions because I was erroneously doing the calculation in my mind of actual revolutions x actual RPM while the software was doing the exact opposite. It is measuring between the marks as one revolution. Since I have two crank revolutions between the marks, it's only counting them as one and thus the RPM shows as half of what the car's actual RPM is.