Clock Range (sometimes Plot Range or Geometric Range) is the range to the target at any given moment. This is distinct from gun range, which is the range entered on the gunsights and which accounts for the change in range during the time-of-flight of the projectile and corrections needed due to the influence of wind along the line of fire.
The difference between clock range and gun range was regarded as so fundamental that the Royal Navy saw fit to ensure that their Dreyer Fire Control Tables were adapted to plot both values clearly by use of separate pencils on their range plots. The difference between the two values in the Royal Navy was expressed as a straddle correction and spotting corrections entered into the Spotting Corrector of a Dreyer table.
- Admiralty, Gunnery Branch (1945). The Gunnery Pocket Book. B.R. 224/45. The National Archives. ADM 234/545.
- Admiralty, Gunnery Branch (1918). Handbook of Captain F. C. Dreyer's Fire Control Tables, 1918. C.B. 1456. Copy No. 10 at Admiralty Library, Portsmouth, United Kingdom.