Garden sundial. This sundial is used to measure time by the position of the sun. The shadow cast on the dial face points to indicate the hour of the day. The shadow is created by the sunlight falling on a triangular piece of slate (top) that sticks outwards from the face. The sun can be seen as a tiny spot reflected on the point of the slate triangle. Here, there are two sundials because the sun is at a different elevation throughout the year. The top sundial is used from 21st December to 21st June and the bottom sundial is used from 21st June to 21st December. Photographed in the RHS Gardens Rosemoor, Devon, UK.