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With the old Skelmorlie Gas Works on the left, the two 'Measured Mile Posts' below 'The Hydro Hotel', for the northern end of the speed trials, show up clearly here Though The Admiralty only started to document steam-ship trials around 1840, Clyde shipbuilders had for long been ‘running the lights’, steaming at full speed the 13.666 nautical mile course between The Cloch and Cumbrae Head lighthouses, the run takes 60 minutes 17 seconds at 13.6 knots and 41 minutes at 20 knots. The problem was one of distance. 
By the time the ship had turned round to do a second, return, run, the tidal conditions, the wind and the weather could all have changed making any conclusions dubious. 
The tip of the landward 'mile post' shows above the pier entrance The answer lay in finding a shorter testing distance, that between the old steamer pier at Skelmorlie, just below the site for Skelmorlie Hydropathic Hotel and southwards to Skelmorlie Castle, this later to be regarded as the most important ‘measured mile’ in Britain - a nautical mile, originally defined as being 6,080 imperial feet, has been redefined and accepted internationally as 1,852 metres, about 10 feet less. Having sought out the agreement of The Earl of Eglinton, who owned the land, John, son of Robert Napier, erected the necessary unlit beacons at Skelmorlie and, on July 4, 1866, George Henry Richards, at The Hydrographic Office of The Admiralty in London, sent out - “Notice to Mariners No 36, Scotland West Coast, Measured Mile in The Firth of Clyde” to the effect that - “Notice is hereby given that beacons to indicate the length of a nautical mile (6,080 feet) have been erected on the eastern shore of The Firth of Clyde. "Each beacon consists of a single pole, 45-feet high, with arms 10-feet long forming a broad ( V and ‘inverted’ V ) angle 15-feet from the base, the whole being painted white. "The two northern beacons are erected near Skelmorlie Pier, the outer one being close to the high water shore on the south side and, from it, the inner one (in the recess of the cliff) is 83 yards distant bearing S.E. by E¾E. "The two southern beacons stand on level ground near Skelmorlie Castle, the inner one being 100 yards from the outer one in a S.E. by E¾ direction. "The courses parallel with the measured mile, at right angles to the line of transit of the beacons, are NNE¼E and SSW¼W. The shore may be approached to the distance of a third of a mile”. Once the ‘V’ and the ‘inverted’ ‘V’ cross-arms were aligned, they became an “X” and stop-watches started, or, conversely stopped, to determine the exact time taken to run the distance between the beacons and the results read off from a ‘standard’ agreed ‘time and distance’ table published in almanacs. Ideally, to bring the ships to a ‘steady state of motion’, ensuring that there were no avoidable changes in steering or acceleration forces on the propellor(s), these distorting accurate speed calculations, ships would always run a straight and steady course for up to four miles before going through the beacon transits. At the end of each run, the ship was turned round and run back over the course at the same engine power and revolutions so as to ‘neutralise’ any effects of tide and wind and an average speed result then calculated for the two runs. It would be customary to make at least two return trips over the course to get an agreed ‘average’ and different methods of calculating ‘averages’ could find results varying by about ½ of 1%. | 
