Now that the projection from the key has been finalised it can be compared once again to the actual physical key that was found in the shaft. If you zoom in to the key area and, with the clock auto started, let the plot develop you can see that the geometry line now perfectly matches the key's left arm.
To ensure that there is no doubt about the validity of this geometry and the mathematics from which it is formed the architects have included a cross checking feature into the metal key. If you look at the right arm of the key you can see that the under side of the end section of this arm is straight. When the photograph of the key is correctly scaled so that the left arm geometry plot perfectly matches the left arm, the straight portion of the right arm aligns with the first stone overlap in the gallery.
From the earlier analysis of the shaft (page C6) when the paint marks on the shaft's wall were considered it is known that the clock can be stopped to align the ascending passage line with the paint marks. Equally it is possible to stop the clock when the ascending passage line is concurrent with the first overlap of stone on the gallery wall. If you stop the clock with the ascending passage line running down the first gallery overlap line you can see that on the left side of the plot the plot point is located at the turning point on the curve.