METHODS OF RECORDING 



to correct for this by injecting a suitable fraction of the time-base generator 

 output into the deflection amplifier, but it must be remembered that a 

 different fraction is required at each change of sweep or film speed. Probably 

 the best solution is to employ a modified cine camera possessing a claw or 



Stimulus n 

 artefacts R^PoH^es 



Stimulus Responses 

 artefacts 



Figure 40.2 



Figure 40.3 



maltese cross mechanism and synchronized so that the film is advanced 

 one frame each time the spot flies back, and is motionless during the sweep 

 period. 



The mechanical time-base method — For phenomena which are slow, or 

 which caimot be evoked at a definite time, it is better to let the movement of 

 the paper or film itself provide the time-base. The electrical time-base 

 generator is disconnected, and either the cathode ray tube is turned round 



Figure 40.4 



bodily on its axis or the deflection amplifier output switched to the X plates, 

 so that the signal deflects the spot at right angles to the direction of film 

 motion. The latter method is more convenient but produces in general a 

 change in deflection sensitivity which may be confusing. The record then 

 has perhaps the appearance of Figure 40.4. 



Film is quite expensive, and not all records that get taken are worthy of 

 retention: conversely, excessively parsimonious use of film may lead to 

 something important being missed. This is the case for the 'intermediate' 



640 



