Question on the performance specs for an old motor

[Craig Putnam]

This is a question perhaps best addressed by those mentors that have been around for some time.

We have a project going (nothing to do with this year's robot) using the DELCO seat motors that we used to get in our FIRST kit of parts. The torque vs. speed graph published for these motors is strange and I need some advice as to how to interpret it.

Basically, one would expect to see a straight line from the stall torque / speed data point to the no-load torque / speed data point. This graph however has what appears to be two lines - parallel to each other - with the area in between being shaded.

Specifically, we have the upper left data point shown as 1.3 Nm @ 95 rpm, the lower left data point is 0.1 Nm @ 400 rpm, the upper right data point being 1.3 Nm @ 310 rpm and the lower right data point is 0.1 Nm @ 615 rpm. The interior area of the parallelogram defined by these 4 points is shaded.

It occurred to me that the two lines might represent CW vs. CCW rotation, but the difference in speeds seems to me to be too great for that to be the case.

Does anyone have any ideas on how one is supposed to interpret this graph?

Thanks.