Newby question. When I was using quick check feature not to long ago, checking the height of 2 plains, and then a couple of weeks later I went and used quick check on the legnth of a part and the dimension came back .236 larger than what it should have been( double checked the dimension with our shop certified caliper).
Sounds like a probe comp issue to me OR a work-plane / alignment issue. You can't just take hits on each end of a part and expect the correct distance-between-points value.
I have had more than one occasion where the dimension I have checked was larger by about or exactly the radius of my probe. I'm not sure how large of a probe you are using, or if you are working off of CAD, but it sounds like a vector issue of the points you have taken, possible on both planes. 0.236" is just about 6mm. Double check the vectors and see how it turns out. Just the other day I found a dimension to a point I was checking to be off by 0.118. Upon further review my vector was pointed 0,0,1 rather than 0,-1,0. I regenerated my hits with the new vector, executed the feature again, and the dimension came in within 0.002". Worth a shot, and a good thing to double check before you report a dimension out of tolerance.
When you're measuring points on a surface with an arm, you have to be sure that your probe is pointing at an angle no more than 90 degrees from a normal to the surface you're measuring, or as Bigguns and Matthew said, the software will compensate to the other side of the probe. If you don't have CAD, use 3 sample hits for your points to be sure the vector is good for the software to figure out what you want measured. If you don't, it will snap to the closest axis based on the angle you're holding the arm. There's a tutorial from PCDmis Portable for the arm that will show you images of how to properly CMM different features (holes, studs, points). The tutorial is somewhere in the PCDMis folder.
You can also do the pull point, but they are a pain in the (posterior). For a pull point, you have to press and hold the measure button, and pull squarly away from the surface, then release the button. You have to do it within 1 second, or after one second, PCDmis asumes you're scanning, and then you just get a bunch of points in space, that you now have to delete. Sample hits and watch your angle of approach is best.
