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we shall discuss again these same questions without tangible results". 
At 5.44 Mr. Harry (Switzerland) took the floor and said in substance: 
One experiment which we have made in Switzerland may have a certain 
interest in this discussion. We have had the opportunity to give the same 
geodetic control and the same pair of plates to four private photogrammetric 
offices. Checking the 1 : 2500 scale topographic plans gave four different quali- 
ties when classified by their mean errors which we called I, IT, III, IV. It chanced 
that the best quality I had been obtained with an old Autograph A2, how- 
ever, the least satisfactory quality had been obtained with a universal modern 
plotter A5. The experiment proves then, that aside from the part of the ap- 
paratus, there is also the influence of the man who operates it and this shows 
a danger of "international organization testing". I am of the opinion that an 
officially recognized international ought to formulate the rules and conditions 
of a test. But the testing of the machines ought to remain the task of the users, 
who have the highest interest and who have the theoretical and practical 
training desirable for research. 
At 5.48 Mr. Schlund (Union of South Africa) requested the floor. Several 
things have struck me in the discussion. Mr. Schermerhorn has said that tests 
on old apparatus have no value. What Mr. Harry said seems to indicate the 
contrary. We have used stereoplanigraphs of different ages and we would like 
to have an official knowledge of their relative value. But what to say of the 
Multiplex? One never knows what one can expect. The photographs 9 X 9 
‘nches are reduced to 44 millimeters square and we ask what we can obtain 
when the plate is reprojected. One thing that controls it then first of all is the 
resolving power of the emulsion. We should ask the manufacturers of the 
Multiplex for tests of precision combined with resolving power to know what 
can really expect from this apparatus. 
5.52 Mr. Schermerhorn took the floor to reply to Mr. Harry. 
One might think that I am in disagreement with Mr. Harry. Not at all. 
The results obtained clearly depend on the operator, but what I do oppose Is 
that one adopts general indications for the apparatus without precise official 
tests. If I do not know what the mean square error in the plane of the negative 
is, if it is 6 or 16 microns for example for a test of aerial triangulation, all other 
statements on the results obtained have but little value whether one is con- 
cerned with old or new apparatus. We have at Delft old instruments which 
have turned for tens of thousands of hours and they are still in service doing 
excellent work. 
At 5.55 Mr. Pennington took the floor a last time to defend his standardi- 
zation project. 
It is fully appreciated that the total evaluation of an instrument 1s a com- 
plex problem which cannot be solved by a few figures. In formulating and 
proposing this test there has been no thought that this would be the sole 
criteria for judging a plotting instrument, but rather that it would provide a 
standardized method of testing and specifying instrument accuracy and pre- 
cison. The suggestion that the test be a complete solution of a cartographic 
problem does not serve this purpose. Prof. Schermerhorn has said that in order 
to evaluate work with a particular instrument, the mean square error in the 
instrument should be known. The proposed or a similar standard test will serve 
that purpose.