"Gantry board" is a kind of pay-off device in early small buildings. It is a door-shaped wooden board with a small width, which is nailed horizontally on the top of two wooden stakes. The height is about 500 ~ 600 mm from the ground, which is used to mark the axis of the external wall.

Matters needing attention and specific operations:

In order to mark the axis position of the wall before the excavation of the foundation trench of the building, gantry plates are set at both ends of the wall axis without affecting the excavation of the foundation trench, and nails are nailed on the gantry plates to mark the axis position of the wall. The line between two nails is the axis of the wall. This marks the axis of the four external walls of the building.

In this way, when digging the foundation trench, the axis of the wall foundation can be determined by the connection of two nails on the gantry plate;

After the foundation is completed, the axis position and elevation horizontal line on the gantry plate can be returned to the wall foundation;

Of course, the axis position of the gantry plate can also be used to determine the axis of the wall.