Hi everybody, here is my modest contribution to the subject, according the old method (thanks to Alain Mory) it is based on finding the local meridian in front of the wall. If the floor in front of the wall is well horizontal you can use it right away, if not you have to put a flat stone or board on the ground & put it horizontal in every way. Lets say the lenght of the board is 65cm in the direction south/north, mount a style of +/- 20cm vertically on the south end of the board; on top of the style you attach a small plate in such a manner that the angle plate/board is = local lattitude; in the small plate you drill a hole of +/- 3mm. With a plumbers weight you find the vertical projection of that hole on the board, that is the first point of the local meridian. Then around 9 in the morning you mark the spot of the gnomons hole on the board; with as radius the first point of the meridian & this spot you draw part of a circle that goes to the right up till the edge of the board.If the first spot was obtained say at 9h 7min or 2h 53min before noon, the image of the sun will appear again on the same circle in a different position, at 2h 53min after noon. So a little before that hour you observe the spot, & when it is on the circle, you mark it. Then you join both spots with a line, determine the middle, which is the second point of the meridian. Prolong this meridian line up to the wall is not difficult provided you do it with a helper to taughten the thin cord & check its position over the meridian.The angle made by this line & the orthogonal on the wall is the declination value of the wall. If you have doubts about the wall being well vertical & plane, one can allways use a marine plywood board about the size of the future sundial, put it well vertical, mark the footprint on the ground with several points, measure the angle to that board & later install that board on the wall in exactly the same position with plumbers weights & glass level. Thank you for reading all this, Walter
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