A pantochronometer is a Horizontal Magnetic Dial, i.e. a floating sundial on a compass card. The rotating card automatically aligns itself along a north-south axis. The system was already in use in the 18th C. Collectors & museums refer to pantochronometers as "Magnetic Dials". The term pantochronometer was apparently coined in the early 19th century by Charles Essex & Co, 28 Gloucester-Street, Clerkenwell, London. Most makers referred to, or labeled them as, "Magnetic Dial" {Porter for example}. Few others referred to, or labeled them also as pantochronometer, and delivered usually, but not always, together with EOT tables (Equation of Time). (info from Compassmuseum.com)
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