150
A line of check levels was run from Kowloon Tong through "Beacon Hill" Tunnel to the Fundamental Bench Mark at Sha Tin. From the Fundamental Bench Mark at Cosmopolitan Dock a network of double levelled lines was run to 69 existing Bench Marks in Kowloon and to two Milestone Bench Mark's (Milestone No. 1 & No. 2 in Nathan Road).
The network was carefully adjusted and if the difference of level between Bench Marks obtained in the field exceeded the difference in level between the same Bench Marks obtained by adjustment, by 0.01 foot the field work was repeated.
27. The values of Bench Marks in Kowloon and New Territories are given as a height in feet above Principal Datum, Hong Kong which is 17.883 feet below "H.M.S. Rifleman's Copper Bolt" established in the Naval Yard. The relation of Kowloon Bench Marks to "Rifleman's Bolt" was found by double levelling from the "bolt" to a bollard on the North arm of Naval wet dock and thence levelling instrumentally (about 5,000 feet length of sight) across the harbour to Bench Mark 64, (a point on Kowloon Station goods loading platform) thence again double levelling to the Fundamental Bench Mark at Cosmopolitan Dock.
This method showed the Fundamental Bench Mark at Cosmopolitan Dock to be 5.351 feet below Rifleman's bolt. Therefore Fundamental Bench Mark Cosmopolitan Dock has been taken as 12.482 feet above Principal datum, Hong Kong and the values of all Bench Marks in Kowloon and New Territories previously obtained adjusted accordingly.
28. The method of levelling instrumentally 5,000 feet across the harbour was as follows:-
The instrument used was Cooke, Troughton and Sims Self Checking Levels, Type No. S113, Telescope power 30, Number Y449. This instrument was set up on the Hong Kong side of the harbour near the bollard on North arm of Naval Dock, mentioned above. A Gayer Staff was held on the Bench Mark on this bollard and a Target Staff exactly 5 feet high from foot to centre of target was held on Kowloon Bench Mark 64.
The instrument was so set up that when properly levelled and properly focussed the central cross hair appeared to bisect the centre of the target. Then the instrument was directed on to the Gayer Staff held on the bollard, refocussed and a reading obtained. Deducting 5 feet, from this reading gave the height of Kowloon Bench Mark above the Bollard. To eliminate re-fraction and curvature errors a similar sight (as soon as possible after the first sight so that weather conditions and consequently refraction might alter as little as possible in the meanwhile) was taken with the instrument set up on the Kowloon side sighting to a Gayer Staff held on Kowloon Bench Mark 64 and to a similar 5 feet high target staff held on the bollard in the Naval Yard Hong Kong.