Normaly your eyes come to the variometer
(VSI) (in french variomètre) every two seconds great maximum. Not only to put your eyes on it, but to correct your altitude
Well I am a bit ancient I guess, and the VSIs that I remember were not IVSIs.
We had to hawk the pitch attitude very carefully and note any trends on the altimeter, then apply a correction to pitch to hold altitude. There was too much lag in the VSI to use it for altitude maintenance. All I used the VSI for was to verify I had set pitch and power about right for a descent rate or climb rate.
It is interesting to learn that there has been a change in scan patterns as a result of new technology.
