Figure 1 shows the underside of the dial plate. The triangular piece is merely a retaining device. With this removed, the underside is shown in Figure 2
The horizontal arm is pivoted at the right hand side, and is driven by the cam just below the centre. This causes the left side, which is attached to the sighting vane, to move up and down, so compensating for the EofT. The cam is driven by the date wheel, the centre of which is the nut at the upper centre. The spring holds the arm in tension.
Figure 3 shows the upper side of the dial plate with the date disc removed - the triangular cam driver is in the centre of the cut out.
This is moved by underside of the date disc which is suitably shaped as shown in Figure 4. One of the serial numbers can be seen here, each dial has several stamped on the component parts of the dial..
Finally, Figure 5 shows the base of the dial with the plate removed - the central nut holds in place a (now rusty) hemispherical washer which allows for the latitude correction via a scale on the base.
Now have a look at the Pilkington Gibbs Sol Horometer
