I forgot to mention that pressure based altimeters will normal exaggerate altitude changes when the barometric pressure is high, and understate changes when the pressure is low.
They are adjusted for barometric pressure by adding or subtracting a constant. (like setting a watch) In order to be accurate, they would need to vary the scale factor, which is fairly tricky to accomplish mechanically. (like how a jeweler would correct a watch that always gains time)
This is easy to do with electronic altimeters, but is not normally done, as it is more important that they track the old mechanical altimeters to avoid collisions than that they be exactly accurate.
Mangosteen: I came across this last night while browsing sites for home weather stations. Definitely reasonably priced and convenient (imho). I have no idea of accuracy or whatever, but if you do not need absolute measurements, it might be a good choice (ymmv, etc, etc…) I have no connection to that site/company, fwiw.
However, when I am actually walking on the property, Google Earth doesn’t help much because the view is from way up in the sky. It gives me a general idea where the high point is on the 7 acres, but not the exact site where the house should be built.
There is more than one high point on the property and rather than just eye ball it, I thought I’d get an instrument to tell me more accurately. Eyeballing is often subject to optical illusions.
I don’t see any “B” showing on the linked map. In fact, the map is so close to my house (maybe a 3 or 4 miles away) that I wonder if the link shows anywhere near where you think it does.
The linked map shows me an area east of Lake Monona, a parking lot right next to an intersections. Am I looking at the same thing you are? That is very flat land. I’ve very doubtful that elevation varies by as as much as 5" anywhere near there.
Are you in Madison? If not, I could go over and snap some pics if you like.
Since I see by an earlier post that you say it is near an ocean, it’s certainly not anywhere near Madison. I’m not sure what the deal is with the linked map in post #26, but it opened up to show me my own city.
The link you put on there is just for the main page. It seems to just load whatever location was the last one you were looking at if you’ve ever used it before (now why was I looking at some piece of scrubland in NW Nevada?). To link to a specific map, you needed to click on the “link to page” button which makes it a permalink: ACME Mapper 2.2
For some reason I can’t get the USGS topo maps to load reliably for that page, but if you can the map that comes up at the highest zoom level is a 20 ft. contour map. That means that every thin line represents 20 ft with darker lines at every 100ft you can read the elevation from (adding or subtracting light contours to arrive at your correct elevation to within about 10 ft.). For example at the coordinates you posted, it looks like it’s a little over 350 feet, since it’s between the 340 and 360 foot contour line, a little closer to the 360 one.
Figuring out where you are exactly when you’re out on the site would be best done by just orienting yourself on the map by comparing the contours to the landforms. Alternatively, if you have a cheap portable GPS, it should be accurate enough horizontally, so you can make some waypoints and then plug them into google earth or that website.
If all you want is the relative highest point you only need the Locke level mentioned by hlanelee. You just choose any point and scan the property for elevations higher than where you are and narrow it down that way. Progressively eliminate all but the highest by moving to a higher elevation and scan around again.
Just a minute here. I think it now becomes a relevant part of the OP to ask you why you’re asking! That is, what the HELL are you planning to build on the home site that a few meters have to do with your decision???
There is a ridge and some trees blocking some of the ocean view towards the right.
We figure if we can find the highest point, a 2 story home should just allow us to see over the ridge and trees (the trees are mature and won’t get any taller).
Building up the land to a slightly higher elevation or building a 3rd floor would be costly.
Why not find the high point with google earth, determine it’s location WRT property boundries using the map scale then physically measure it off with a 100 ft tape and a magnetic compass?