This laser does not draw a line, but five points. It's self-leveling (you really want that in a laser if you use it a lot) and makes perpendicular, level and square horizontal and vertical dots. Accuracy is 1/8 inch at 30 feet (3mm at 10m). Operating range (theoretical) is 100 feet with a detector (not included). Batteries last approximately 30 hours. Point laser diameter ≤ 4mm at a distance of 5m. What are you? If you are using this on the ceiling and want them to be in a straight line you can mark that on the floor and then use the laser to mark a spot on the ceiling to mark where your light will go 90 degree Walls using the 3/4/5 triangle method Makes laying corners much faster Also allows one person to align walls with support posts Also makes wall alignment easier Mount this on a tripod (not included but fits my camera tripod ) and then rotate to show the height on the wall. This can save you a lot of time. Green laser is much more visible than red one. Can be easily seen indoors 45 feet away. Outside, things are a lot more complicated, although I was able to use this to get to a 30 foot deck lane with a bit of fishing (with a big white poster) on an overcast day. It's very solidly built and comes with a HUGE case (I don't know why it's so big). Comes with a well-made carrying case for your belt (but it's quite heavy to carry on a belt). It has a PS rating of 54. They are first rated for dust tightness (scale from 1 to 6), so it's a 5, which is dust tight enough, which is important in a workplace. And the second number is a 4 on a scale of 1 to 8 for water resistance, it can use a small amount of splashing but that's about it. If you drop this in a bucket of water all bets will be void. More/better instructions needed. I even struggled to remove the battery cover (squeeze the tab on top while pulling straight. The instructions in the pictures (I've attached them) leave a lot to be desired (the unlock switch is on one side and you move it) . )