Measurement of HI with a metric steel tape - ? of Does it Matter?
Measure it BEFORE you set up and you can get really really close.
As professionals we should be eliminating as much error as possible, From a practical standpoint it probably doesn't matter.
My thought is that I will do it to the best of my ability. Measuring your HI takes very little time so why not?
Hmm, maybe I have a collectors item, use it every time I have to measure up an HI on the robot.
Several years ago when Ky. was going thru the "gonna switch to metric" phase, I was in the local farm store and saw this laying on a table in it's wrapper with a $12 tag on it. I know the owner pretty well, so I handed it to him and asked how much he would take for it. When he said it's $12 I told him to look at it closer. He flipped it over a couple of times, handed it back to me and said "Here, just take it".
I think it is important to make a distinction between the types of error in reading the HI. If it is a random error of 2mm reading the tape from time to time then it probably doesn't matter too much. However if it is a systematic error of 2mm (which was the original poster's question) it does matter in my opinion. If you deliberately add 2mm to your total station HI only, you will see a noticeable increase in your vertical backsight errors.