## The reference line

The reference line serves as a benchmark for the duration of the work. It is the basis to determine all other measures.

One might be tempted to take as a reference the facade housing against which the pergola will be contiguous. But a façade is rarely well straight. May be dips and bumps. Then it could get errors in positioning depending on the location of the facade from which we take our measure.

It will draw a new reference to a few inches of the front line. This falls well, this pergola model must not be pasted against the facade but detached from 10 cm (edge of the beam-carrier). It adds the width of the beam-carrier B and it gets the distance from the wall to the poles or X 1 = **13.8 cm**. It is at this distance we trace our line of reference. And the Poles against the facade are aligned on the line.

To draw the line, took two measures of X 1 = **13.8 cm.** from the edge of the façade. The two points are remote as possible.

## 1St line perpendicular

This line forms the right edge of the pergola. It is important to be precise on the path and achieve a perfect perpendicular. Can be used a square of macon has the advantage of simplicity but is not very precise. However, the method "3-4-5", a little more technical to get good accuracy.

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**The method "3-4-5" :**

According to Pythagoras, C² = A² + B². Where C is the length of the diagonal, A and B two perpendicular lines.

Or, he is as 5² = 3² + 4² (25 = 16 + 9).

This means that if a diagonal of 5 m connecting two lines 3 and 4 m, then these two lines are perpendicular.

Specifically:

- on first spotted a line of 3 m on the reference line (if your rule of Mâcon is 4 m) or 4 m (if your rule is 3 m).
- Then it positions macon rule roughly perpendicular to the 1st line.
- With a metre to Ribbon, or at best with another rule of 5 m macon, it positions the diagonal to the two lines.
- It adjusts the rule of Mâcon and the diagonal until it measures 4 m and 5 m coincide. This requires a bit of successive adjustment but through trial and error while finesse, it gets a good accuracy.