Hi, my name is Rami Tamimi. If you've ever wanted to be able
to measure elevation accurately and without using any equipment that requires batteries,
of the elevations between several points. All it consists of is starting out at a base point
known as the benchmark. This benchmark has a known elevation that we begin all of our
measurements from. This benchmark is usually a known location that either you or a surveyor or
some government municipality set and provided a record of information that everyone must follow.
For the purposes of this experiment, I'm gonna be using
a point that is on the front side of my house. We'll be using this manhole to begin our level
loop. We have a known elevation on it and it's our benchmark for the project. So what exactly
is leveling? And what kind of measurements are we taking? With leveling, we're starting at a
benchmark that has a known elevation. Whoever is operating the instrument, will hold the instrument
at a distance between the benchmark and the point they want to observe. Another person will then
hold a rod that has numbers on it. These numbers are also subdivided on the rod. The person holding
the rod will first hold the benchmark. Once holding the benchmark, the instrument operator
can then see the difference between the ground elevation and the line of sight of the instrument.
This number is then added to the elevation of the benchmark giving us the instrument height. Now
that we know what our elevation is based off the benchmark of the line of sight of the instrument,
we're then able to turn the angle to another point. This second point is the
foresight. The number that we read from this is the difference between our line of sight and where
the elevation of that point is. Therefore, we subtract it from our instrument height,
giving us a new elevation on a new point. If we're trying to do this on several points,
then we're going to be doing multiple foresights. This could all be from the same setup if you're
able to see all of the points from where you're set up. However, more times than not,
you're gonna want to see points that you can't visibly see at the setup that you're at. So what
do you do? You then have to take a turn point. This turn point can be a feature on the ground
or a physical disk that's dropped on to the ground. You then take a foresight reading on that
and calculate the elevation. After that, you pick up your equipment, you go to the new setup and
then you backsight this last point and create a new setup and start to recollect your data. After
you've finished collecting all your foresight readings, you're gonna want to go back to the
original benchmark and close the loop. You should find that the elevation is relatively close to
the internal recorded elevation. In the office we will then calculate the error in our closure
and redistribute the error so that our elevations are adjusted. This might seem confusing, so we're
gonna do it together right now. [♫Music♫]
Now the first thing you need to do when you first figure out where you're going to be set up,
lay the legs down and step on them so that they're embedded into the earth.
[♫Music♫] Then what you're gonna want to do is level out
the level so that it's completely flat with the horizon. You don't want your level to be tilting
up or tilting down in any way, shape or form. The way that this is done is using these three
knobs. There's one here, and there's one in the back here. These two are used to tilt the level
left and right. The front knob here is used to then tilt the instrument forward and back. The
way you can tell if an instrument is leveled is by seeing this little bubble inside of the glass.
The way that you can see this bubble is by looking into the little mirror. Now when I rotate left and
right, I should be able to adjust the bubble to get into the middle. And then I'll bring it down
just a little bit. Perfect. Now you're going to have somebody holding this rod. This rod is called
a Philadelphia rod. Let's open it up for you guys. This rod is tall. This one I think is 15 feet.
I've only got about eight feet of it opened because I don't think I'm gonna need
to use anything more than that. What you see here are red numbers and black numbers. The red numbers
are entire feet that are being measured from the bottom of the rod. This is where our elevation is
being measured from and that's why it's zero on the bottom. When reading this rod, you're
probably gonna fall somewhere here in the middle. These are feet as well. You're not gonna be able
to see that five or that four down there. Because this might be all you can see in your view finder.
So knowing that this is four feet, you can then try to figure out the tenths and the hundreds. So
we know that we're at four feet. If we're taking a reading and it comes up right at the top of this
line, then we know that our reading is 4.50. However, if the reading comes in right here
at the bottom of the next top line, then our reading is 4.51.
4.52. 4.53.
4.54. 4.55.
As you see, the five is a little bit longer. That's a good indication that you're halfway.
4.56 4.57
4.58 4.59
The bottom line of the number is .09. 4.59, 4.60.
If you get a reading right here in the middle and it's hard to judge whether it's up here or down
here, make the assumption that it's lower. Always make the assumption that it's lower.
That's it. That's all you have to do to read this rod. Something to keep in mind of when you're
holding this rod -- you want to make sure you're holding it straight, not like this, not like this.
Not like this, and not like this. You want to hold it as straight as possible so that the
person sighting you can see the true difference in elevation between where they're at and where you
are. In order to do this properly, all you want to do is swing this back and forth ever so gently. In
doing that, the person reading the rod is going to see a variation in number. They're going to take
the lowest reading that they can see. The lowest reading indicates that the rod is exactly plumb
and where it needs to be rather than being too forward or too back. By doing it slightly,
back and forth, barely touching the rod, you're allowing the reader to see if there's any type of
error. On their end they might not see anything. However if it's a windy day or you just don't have
the ability to hold this thing straight, this will help you do that. You're gonna see a few knobs
on this and they're not very difficult to work with. This right here which is complemented by
another one in this side, are just your turning knobs. These will do a fine turn for something
a lot more precise than your fingers can do. As you can see, while I do this, it's slowly turning
the instrument. All right. That's enough. The next knob you're gonna be interested in
is this one. This is the focusing knob. So when you're sighting something, it looks blurry;
this will allow you to focus in and out. The final knob that you might not realize is on
here is this one. This right here is used to fine tune your crosshairs so that you can
accurately see where the center of your scope is. This will all make sense once we take a reading.
Let's take a reading on our benchmark and begin our leveling project.
[♫Music♫] Looks like a four
up there. Okay so we are at three feet and the crosshairs -- are coming in at
8 point -- looks like laying right on the 3 line right there. So that's gonna be 3.83. That is our
backsight reading on the benchmark. All right. Now we're gonna take our
rod and move it to another point so that we can go to our sight.
So now we're gonna be having a turn point right over here. It's on the bottom of this gate.
I'm gonna be holding the rod. Right here.
And that's where we're going to take our turn. Usually there should be a point here that
we're taking a turn on but for the sake of this experiment, I'm just gonna use the same location.
[♫Music♫] And it looks like we're reading 4.5 -- oh --
I'm gonna go ahead and round that one down to 4.50. Remember if you're coming in between two
numbers, always round down. Chances are the rod is being held just slightly off center
and you're better off reading the lower number. All right. We're gonna go ahead and pick up and
go down to the next setup. [♫Music♫]
This should do right here. Go ahead and step on the legs.
Go ahead and level this thing. Looks pretty good.
It's also a good idea that actually you level, to tap the top just to kinda make sure that
everything is stable. [♫Music♫]
All right now that we have our new setup here, we're gonna backsight
the last point that we just shot and that's going to be our new reference benchmark for this setup.
Here we are. [♫Music♫]
All right and when I look into this, I'm seeing a 3.7---looks like it's right on the 3 line. So 3.73
All right now we can start shooting in some points that we have here on our
sight. Remember from the last lab, we had three points that we set.
Orange, blue, and green -- we're going to be taking the elevations of those points
using this level. Let's start with orange. [♫Music♫]
All right. And it looks like we are getting 5.9 -- oh -- 5.97. Right between that 8 and 7 so I'm
gonna go down, so 5.97. All right.
Next let's measure blue. [♫Music♫]
And it looks like here we're getting 3.19. See how easy that one was? 3.19.
And now the last point we need to measure is point green. Come on let's go. Nice. Slow.
He's really slow. [♫Music♫]
I think we should fire him honestly. He's just a mess. All right, you good? All right here we go.
[♫Music♫] And it looks like we're getting a reading
of .... 5.32. 5.32. Good.
All right. Now that we're done collecting the data here in the field, we need to go back to
our benchmark. So I'm gonna go ahead and turn back to that point at the gate. I'm gonna move
the instrument over to where we were before and then I'm gonna take another reading on the manhole
to verify our elevation. [♫Music♫]
as well as finding the error in our measurements so that we can distribute the error and adjust