Steve,
The chart that you're using for weight measurements is for beef cattle. Your calf is a dairy and I believe that will make a sizable difference (correct me here someone if I'm wrong). Our older steer is a Holstein also, same situation as you, big dairy farmer not interested in the males. Anyway, I compared my records using the chart you were using and found a huge difference. For instance: at 7 mo, by my calculations he weighed about 581 lbs., the chart you using shows him as 1260 lbs, not possible for Norman! This is the formula I've been using (with a regular tape measure)....
Heart girth X Heart Girth X Body Length divided by 300 = weight in pounds. Body Length is measured from the point of the shoulder to the point of the rump(pinbone). And heart girth you already know.
I don't know if this approach is better, but the results seem more reasonable for our calf. Let me know what you get.