You cannot set subgrade elevations for horizontal planes ie. Driveways, parking lots, building slabs with a pipe laser or pitched plane laser. They operate on a linear axis. If you deviate from its tilt axis you will get elevation distortion. You need to use a level plane laser and set elevation points for formwork, expansion joints, keyways or temporary elevation pins to facilitate concrete placement. At a 2% grade you are right that you slope 0.1’ per 5’ (1 ¼ per 5ft). If you are pouring a driveway with no crowns or valleys it’s a simple process of multiplying the length of driveway by .02 and setting elevation stakes. For example if your Garage finish floor is at 100.00’ elevation and you have a 200’ straight driveway sloping down the elevation you need to set at the end is 96.00’ (200’x-0.02= -4.0).

Your absolutely right. The laser has to be positioned over point a or b. Unless someone knows something I don’t know this video is totally wrong

*accurate instrument for leveling, easy for my employees to use not a lot of bells and whistles , less likely for them to screw up*

For a one time setup and not having a pipe laser your will need a point C. Obviously your not going to set up your laser where you plan on excavating. I suggest a 10’ offset to establish point C in line with point A and B (unless you have a derelict operator then you may need some more distance to avoid damage to your instrument) . For this example we will assume a 100’ long sewer line at a 1% grade. Lets say we have an uncovered sewer line leaving a building at a flow line elevation of 100.00’(Point A) and we have to punch thru a manhole 100’ away (Point B) at a 1% fall making our flow line penetration at 99.00’ (100-(100x .01). If we establish point C 10 feet behind the MH and in line with the tie-in (point B to A), we have now established a horizontal difference of 110 feet with a corresponding vertical rise of 1.10’. We can set our laser up over point C and then take a level reading over to point A. Once we get a solid tone at A we can set our linker rod (let’s make it easy and set it to 100.00) and then raise the sensor 1.10 feet from this point. Your Tape should read 98.90 (this may seem backwards to those that are used to a tape measure or a Philly rod vs. a linker rod). Now that the sensor has been elevated, have a 2nd person adjust the slope upwards until you get a solid tone on your sensor. Once you have established this, you have now established your base line slope. You can now extend your rod down to the flow line of the sewer pipe and adjust your sensor for a solid tone and you are good to go. You can now proceed up and down the ditch line without adjusting your sensor for flow line elevations.

This video is misleading. The slope being discussed is the rise and/fall (ie 100 mm) over the distance from the laser to point B, and not a 100 mm fall between the points A and B.

Doesn't the laser have to be positioned directly over the top of point A? The rl-h5a manual suggests so. I used this video to attempt to set up slope for the first time and found the video to be misleading regarding where the laser could be positioned in relation to point A. After a lot of wasted time I referred to the manual which differed from this video.

حق

Isn’t there some math required? I’m trying to sub grade driveways that are 26 feet long with a 4 in slab. A coworker told me that I can use the laser instead of string, I know this but I have to adjust the finder on the rod every few feet to find my grade. For example, if I want to find my grade on a 2% slope, I need to move the finder on the rod one tenth every 5 feet. Is the method in this vid supposed to help me so I don’t have to calculate my position all the time to find my grade?

How much?

This video is incorrect on how to set up a slope laser.