Declinatory construction dial for latitude 49° 31' North. The dial consists of a semicircular wooden plate. It has a semicircular degree scale marked with tiny brass nails. The brass compass set on the meridian line of the plate is a French replacement (probably eighteenth century). It has a degree scale and sixteen points named by French initials. Pivoted to the centre of the semicircle is a wooden index arm. It carries a small, rectangular, brass horizontal sundial. This has hour-lines radiating out from the base of the simple shaped gnomon.

If a degree of declination needs to be known, as it does, for example, in the erection of a mural dial, it may be measured by this instrument. Such instruments were widely used and illustrated in many texts on dialling. The compass on the present instrument is a French replacement. The latitude given on the dial-plate above the gnomon (49 30') suggests that the dial was made in Nuremberg (latitude 49° 27' N).

For more information regarding this dial please refer to the OUP & NMM catalogue, 'Sundials at Greenwich'.