- 1 - 
LATEST DEVELOPMENTS 
RELATING TO 
THE HILGER & WATTS STEREOCOMPARATOR 
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Summary 
The principle features of the Hilger & Watts Stereocomparator 
are described together with the modifications and improvements 
which have been introduced as a result of gaining user 
experience. The advantages of the solid state decoding and 
transmitting system are outlined, and the forms of recording 
by punched card or teleprinter are given. 
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The Hilger & Watts Stereocomparator was developed originally to 
meet a War Office requirement for a measuring machine with automatic 
recording of photo - co-ordinates and pre-set data. The prototype has 
been fully described by A.H. Anstis (l), but since then a number of 
changes have been ma.de to the production version. Though very little 
alteration has been made to the specification or the principle of the 
mechanical design the overall appearance has undergone quite a change, 
and there has been considerable development in the recording system. 
The first production model, which would, perhaps, be better des 
cribed as a second prototype, was shown at the i960 I.S.P. Congress 
Exhibition in London (still with a relay-operated recording system), 
and described in a general review of stereocomparators by 
I.A. Harley (2). All the development effort devoted to the project 
between prototype and final production model has been directed towards 
obtaining full user convenience, good mechanical functioning and accu 
racy, and reliability in the digital recording system. Too much empha 
sis, of course, cannot be placed upon the importance of the latter, and 
the decoding and transmitting system now uses transistor switching 
throughout, the advantages of which will be discussed later. For the 
latter part of the development period the Ordnance Survey operated a 
machine under test, and the assistance which they gave, both as an 
organisation and as individuals, was of very great value indeed, and 
has, in no small way, contributed to the successful development of the 
final model. In this short account of the latest developments it is not 
proposed to give a complete description of the machine, which has 
already been done by Anstis and Harley, and may be obtained from Hilger 
& Watts literature (3). 
The fundamental specification was drawn up almost ten years ago, 
by those with the foresight to see that reseaux photography offered 
significant advantages for analytical photograrametry. We can now see 
an increasing interest in the reseaux, Judging by the number of manu 
facturers offering cameras with this facility.