(HP-65) Horizontal Sextant angles to Rectangular Coordinates

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An extract from A New Station Pointer - The Hewlett-Packard HP 65, Commander J.B. Dixon (R.N.), International Hydrographic Review, July 1976

ABSTRACT
The Hewlett-Packard portable calculator HP 65 can be programmed to convert the two angles of a horizontal sextant angle fix into rectangular coordinates ready for immediate plotting. This method of plotting fixes is easier, quicker and more accurate than the traditional station pointer.
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CONCLUSION
Station pointer habits die hard, and it takes time for the mind to forget them and become adapted to the calculator. In particular a mental effort is needed to remember which marks’ coordinates have been keyed into the addressable registers. But the HP 65 is useful to the surveyor in a multitude of different ways, many of which are not apparent until it is owned and its capabilities fully understood. For instance, with slight alterations, the above programme can be used to solve a theodolite resection prior to the semi-graphic stage. Eastings and northings cannot be displayed simultaneously, therefore one is stored in the y register of the operational stack and the other displayed in the x register; they are exchanged by pressing key E. The 8 seconds running time of the resection programme seems an age when waiting to plot but there can be no doubt that it is quicker, as well as being easier and more accurate, than using a station pointer. For large scale river and dock work a boat’s course is often carefully controlled along the predetermined sounding lines, but its track may still be recorded by frequent sextant fixes which cannot be plotted at the time. The tedium of plotting all these, on completion of the day’s work, by station pointer, or the delay in waiting for the angles to be converted into rectangular coordinates by a distant computer are both avoided with an HP 65. The author’s present hydrographic work sometimes involves sounding from a locally hired boat, and it is a big advantage to be able to plot straight onto a rectangular gridded sheet and not to require a plotting table that is solid enough for a sounding board and station pointers.
The HP 65, with the impressive capability built into its small size, effectively enlarges the scope of inshore and coastal survey work controlled by the sextant.

Includes illustrations, figures, equations, descriptions, explanations and fully commented program listing.

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