I had to do a speedometer-like drawing in OmniGraffle. I wasn’t sure how to do that well, so I asked on the OmniGraffle Users Mailing List. With a little help and pointers in the right direction, I got a good representation.
The trick was using the Arrange in a Circle script. I created a rectangle that was basically very narrow and filled black to represent one of my tick marks. Then I duplicated it 20 or so times. I used the script to arrange them in a circle of diameter 200. I selected the intermediate tick marks and made them gray and a little shorter than the main tick marks. The rest is window dressing. The red arc is problematic and a bit of a hack. It’s a red circle with a bunch of white circles and white freeform shapes hiding everything except the bit of red that I want. Here’s the Speedometer Graffle. It is released to the public domain.