Fig. 2. Precision with which electric organ discharge (EOD) current could be shunted at a selected phase within a single EOD. (A) Oscillogram showing accumulated recordings from 100 successive tests in which the switch was closed for 100 µs in a preassigned phase. The upper trace shows the rectangular reference pulse that marked the `onset' of the EOD and triggered the recordings. The middle trace shows the head—tail EOD with head-positive deflections going upwards. The lower trace shows the current that flowed through the external circuit during switch closure. As a result of a variety of factors (see text) the recorded EODs jitter with respect to the onset-mark and the current signal. However, note that a reasonably small phase jitter could be achieved. (B) To assess the phase stability quantitatively, for each of 1000 successive experiments a precision counter measured the time between the rising flank of the reference pulse and that when the falling phase of the amplified EOD had reached a set threshold (time interval as defined in A). The histogram shows the distribution of recorded values for (relative to a reference value of tr=476.5 µs; bin width 1 µs) as obtained in 1000 successive experiments. Note the small amount of phase jitter (S.D. ±10.4 µs). The structure of this distribution is probably determined by different major resting positions of the fish assumed during the 1000 experiments.