I'm having a hard time figuring out how to determine elevation WITHOUT knowing the HI...
Let's say you have a benchmark of 100'; you set up your level, read the rod and it says 5'; you set the rod on a TP and it says 6'. This is easy math, that you do in your head, and the TP is 99'. But didn't you add 5' to 100' then subtract 6' from 105'? I must be missing something...
Never invert rod to shoot any electric device, pole, wire or other.
This practice has caused several surveyors death by electrocution.
I'm having a hard time figuring out how to determine elevation WITHOUT knowing the HI...
Let's say you have a benchmark of 100'; you set up your level, read the rod and it says 5'; you set the rod on a TP and it says 6'. This is easy math, that you do in your head, and the TP is 99'. But didn't you add 5' to 100' then subtract 6' from 105'? I must be missing something...
You did it exactly how I would do it. In my head, I add +5, subtract -6, so that's negative 1, giving you 99 ft. I don't have to write 105' in the book to get to 99'.
My question was, why do I need to write the intermediate HI in a column. Others have answered why (ease of math essentially and lessening the chances of error further down the line it seems). The way I have set up my Excel spreadsheet I don't even use the HI column in determining the elevation values. ?ÿ?ÿ
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Use the H.I. ?ÿThe way you are doing it takes as many steps and increases the chance of a sign error. Basing field practices and calculations on Excel spreadsheets is a bad idea. It should work in the reverse.
You are right. My choice of example was the result of a lack of imagination (and consideration of the danger). There are many ways to accidentally maim or kill yourself by not paying attention to potential hazards.?ÿ
Mea culpa.
Establishing height of flagpole introduced me to the procedure.
I will be great full to nrver own or use a level again?ÿ
Inverted rod would be used to measure building height and other matters that are above the practical location of the instrument.?ÿ
I recommend that the OP learn the basics of fire hydrants. Top of hydrant may indicate different things in various parts of the country. I use a head bolt rather than the cap screw which can and does move vertically from time to time. I've seen elevations established on the top of the pumper port and flange at the base.?ÿ
For what its worth, I always book the HI.?ÿ
If you use a fire hydrant for a short term purpose you may be ok.?ÿ
Discussion on this or previous forum pointed out that they tend to move more than you might suspect.
And one case was cited where a new shopping mall got graded from a hydrant elevation before anyone realized the city had replaced the hydrant with a shorter model.?ÿ Very expensive to fix the drainage.
So the need to verify hydrants is greater than many other points that might get used.
Discussion on this or previous forum pointed out that they tend to move more than you might suspect.
There's a reason they pour thrust blocks beneath fire hydrants.?ÿ The thrust block doesn't guarantee that the hydrant won't move at all, it just keeps the pipe from breaking.
In the 60's they set a series of bench marks on fire hydrants around town, the northmost flange bolt. By 2000 most were all still intact and still holding good elevations. Always check between them of course. Now we don't use them cause we have plenty of our own and there have been many replaced through new street construction.
