Laser Level Recomendations? Need To Sister Sagging Floor Joists

I have to do some under-the-house work sistering floor joists to correct a pretty serious sag. (any pointer to a place to get info. about that would be appreciated.)
A guy was telling me about a laser leveling system he got at Sam's Club for about $60 that came with two things to hang on opposing walls and would easily work for what I need to do.
Any recommendations? Brand names? I saw a single unit that put out lasers in 4 directions and vertically, but it was $200. Would something from Harbor Freight be good enough?
Thnaks in advance for any advice.
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A couple of tight strings will get you what you need at almost no cost! If the joists are not level at each end the laser level will just make the situation bug you more! A string pulled tight below the joist will give you a straight reference line to use to get it all straightened out. Greg
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Overkill, as mentioned. Rough carpentry is just that: rough. I'd find a straight couple of joists(or even slightly crowned), trim them to size, and sister away. Tom
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Recent article in either last or this months Fine Homebuilding on all the options to correct sagging floor. Everything from sister joists to new supports with lots of other interesting options.
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Overkill. As another user suggested, just use a string. There's no guarantee the supports on each end of joists are level to start with.
If you really want level, just pick up some clear tubing and make a water level. Cheap, reliable, and easy to use. It also works around corners or behind obstructions, something a laser can't do.
We used a water level to build the foundation of our house and garage. They work great.
I like to stick one end of the tube in a bottle of water and secure that so it can't slip out. It's easier to use than just trying to balance out the two ends of a tube.
Be sure to bleed out any air bubbles before you start taking measurements.
Anthony
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