How do I lay a deck level in relation to the house wall?

[Johan Larsson9794]

As previously mentioned "Muraresnöre" !!!
Completely superior, the other method is to flukta = look with one eye and make a mark.

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When the yellow lines, going from the inner point of one green to the outer point of the other, are equal in length, it is perpendicular, provided that the green lines are of equal length. 😉

I must have missed this part in elementary school…

Ok, so if I have two equally long beams (green) and adjust them based on the "cross" (yellow), when the two lines of the cross are equal in length, then the beams will lie in exactly the same line (i.e., straight) as the house's facades?

 

[FredrikR]

Must have missed this part in elementary school...

Ok, so if I have two equally long bars (green) and adjust them based on the "cross" (yellow), when the two lines of the cross are equally long, then the bars will be in exactly the same line (i.e., straight) as the house's facades?

Perpendicular to the facade. ✅
The same applies for the 3-4-5 variant.

Tying up a mason's line as mentioned and sighting against it is also convenient and easy to use.