Stewart Warner vacuum gauge was not steady at idle

Back when my parents purchased a special order '71 383 equipped Plymouth (road runner), I had our local mechanic install a couple of accessory SW brand gauges, manifold vacuum and oil temperature. However, the vacuum gauge always bothered me because at idle (around 12", if I remember correctly), the needle would kind of vibrate, shake, well, you know, it was not steady. At cruise speed it would not do that.

Now I am considering the addition of a vacuum gauge to one, two, or three of my project vehicles ('72 Satellite, '65 Formula S, '65 Signet convertible). I wonder if I will run into the same problem as before?