Odometer adds mile at 9/10. Is this common?

My odometer on my 1985 245 shows 230,000 miles and some change. Everything on the cluster works, except the odometer adds a mile with the gauge hits 9/10. Not during 9/10, but a solid new mile when 9 out of 10 hits. I did a calculation that 9 out of 10 = 0.9 and 0.9 X

So, if this odometer has done this since day 1, then it's about 27,000 miles over. If it's done it since 100,000 miles, it's about half of that over.

Any ideas?

Jamie