A two channel display format is illustrated The second channel , labelled C2, is plotted above the first, labelled C1. The left hand trace shows the amplitude distribution of the signal on a logarithmic scale. The axis ticks are at 1,10 and 100uVpp and dotted graticules are in ratio 1,2,4,6,8. In this case it is a steady calibration signal at 100uVpp. at 10Hz. The CFAM3c amplitude can write down to 0.52uVpp and up to 400uVpp, the latter extending above the marked amplitude scale limit of 200uVpp.
On the right hand side there are a number of bands. The distance marked M between graticules represents a muscle signal amplitude of 50uVpp. This trace plots from left to right. This is so that any increase of muscle activity points towards any corresponding artefactual increase of energy in the Beta band, plotted to its right.
The distances marked B, A, T, D, V between graticules represent 100% of energy in each traditional EEG frequency band, Beta, Alpha, Theta, Delta, with an additional band Vlf for <1Hz. In this case for a 10Hz calibration signal, 100% of the signal energy is in the Alpha band. These traces are plotted from right to left. A single line, representing a weighted mean frequency measure, overlays the percentage frequency plots, the frequency range is 0.5 to 37Hz.
S is the percentage time the signal is below 1uVpp, so the distance between graticules again measures 100%. The trace is plotted from right to left.
The electrode impedance is measured up to a maximum of 30Kohms, each graticule represents 10Kohm. In this case the 10Hz calibration signal is from a 10ohm source impedance and so is shown effectively as 0 Kohms on the trace. The impedance trace is plotted from right to left.
L indicates the amount of mains frequency (line) interference. It measures up to 100uVpp and writes from the right hand edge towards the zero ohms graticule.
Between the amplitude and frequency plots E indicates the event marker output. Each event marker is turned on, and then off by successive up/down arrow keys with the Event button highlighted. Events are numbered consecutively up to 999. If two events occur within one 2 second epoch (at 30cm.hr) they will be amalgamated into one (at 6cm.hr the epoch length is 10sec). If two events are shown on the screen but are so close that their numerical labelling would overlap, only the first is labelled.
At the left hand edge of the amplitude plot the time ( 24hour clock) is written next to each horizontal graticule. For a chart speed indicated as off, or 30cm.hr, these graticules are at 1 minute intervals. For a chart speed indicated as 6cm.hr.these intervals are 5 minutes.
Below the amplitude and frequency plots, at the bottom of the screen during recording but not illustrated here, are written in boxes the current values in micro-volts peak to peak for 50Hz LINE interference, MUSCLE activity, and electrode impedance (KOHMS). These are shown numerically, one value for each channel. The channel sequence is left to right, lowest numbered channel to the left.
At the left of the above is a box labelled CUTOUT. When an input voltage excursion exceeds the limits of the input amplifier, the recorded signal cannot be digitised accurately. In this case, to the right of CUTOUT is written the number, or numbers, of the affected recording channel(s). Additionally, since there is no reliable input data in that channel, the LINE, MUSCLE and KOHMS values for that channel are replaced by question marks. The data in the boxes are also then written white on black. Further, the CFAM3c amplitude-frequency plot is not written in the 2 second epoch (10second epoch at 6cm.hr) in which the CUTOUT occurred.
The head diagrams show the recording electrode positions for each channel. The conventional EEG 10-20 electrode labelling system is used. The letters AH indicate that the channel is being recorded for amplitude-frequency analysis. The letters EP indicate that the channel is being used for the computation of averaged evoked potentials. Half of the line showing the electrode position on the head diagrams is in practice coloured red for the positive input. This matches with the head-box input connector colours. A green circle also indicates the position of the independent electrode.
