1150 
MONITORING 
A. SCRIABINE, Merck Institute, West Point, 
Pa. : Are there more accurate transducers avail- 
able? 
Dr. Konigsberg : Yes, they are. We have 
been making them on special order only so far. 
But we do have them available v^^hether single 
or multi-channel. I do want to make one more 
comment about this 0.1 mm accuracy. If you 
will take these large numbers we have been 
throwing around, divide them by 30 days, and 
you can get something like a millimeter of drift 
a day with one of the worst systems down to 
0.5 or 0.1 mm drift a day. 
In the measurement of cerebral spinal fluid 
pressures in the brain, where the transducers 
are put in and calibrated over a three to four 
day period, it is important to measure very low 
pressures. It has been commonly reported that 
stability on the order of a millimeter of mercury 
a day is achievable now. So it all depends on 
whether you want to know two months from ' 
now your pressure to within a millimeter of ' 
mercury or you can calibrate immediately be- 
fore and after an experiment because a dra- j 
matic change is not going to occur in a day. 
Thus, if you are making a study and you can 
calibrate or get a few calibrations, you will get i 
some kind of a line connecting your points. You ' 
can have some reasonable assurance that you i 
are accurate to within a few millimeters of 
mercury, if you can stop the experiment, sacri- 
fice the animal, and calibrate your transducer. 
You will not be positive about what happened 
several hours or days ago, but you are going 
to be reasonably close. Now, this does require 
technique ; it is expensive ; it does require care. 
But the thing that is most important is, except 
for a few bad actors, that these random shifts \ 
do not occur. They are, in general, systematic 
shifts. 
