The cursor choice control sets the mode in which the cursor operates. Initially it shows "Cursor". The default cursor mode is in operation.
If you are viewing an EEG and click on the display a vertical cursor line appears. By holding down the mouse button and dragging sideways you can move the line to position it accurately - say on the peak of a spike. This line will stay unchanged if you alter the montage, gain, time constant or HF filter.
If you change the Xscale ("paper speed") then the sub page displayed will always show the cursor (in the same place on the record although in general not in the same place on the screen).
In the illustration on the right the vertical cursor line is indicated by the red arrow. If you look at the second picture you will see that the line is in the same place relative to the displayed waveforms although the trace has been expanded.
This allows you accurately to compare the appearance of the waveform under different conditions. If you view a different page then the cursor line disappears.
The classic way of measuring the amplitude of rhythms in the EEG is to use a transparent cursor with horizontal lines ruled at 0.5 and 1.0 cm spacing - corresponding to 50uV and 100uV at the usual gain of 10uV/mm.
The amplitude cursor is similar.
Select "Amp" from the Cursor choice control
Point to the waveform (or trace) to be measured (it is usually best to expand the trace to, say, 50 pixels per second) then drag downwards to create an amplitude cursor.
Two horizontal lines appear which as you drag downwards become separated in successive jumps (you may have to wait a little while for the 'drag' to take effect, Note: the pointer at this stage will be outside the rectangle formed by the horizontal lines.) corresponding to 1, 2, 5, 10, . .etc units. (uV, mV etc)
Select a convenient spacing and then release the mouse button.
In the 'measurement display area' a message appears
Channel xx Measure= nn Units
To measure a section of trace place the pointer between the horizontal lines, depress the mouse button (the cursor will 'jump' so that the pointer is at the centre) and drag the whole cursor over the waveform of interest (again the response to the drag may be rather slow).
To create a new cursor simply repeat the procedure anywhere outside the existing cursor lines.
This cursor behaves like the simple cursor when changing the Xscale. Note that the spacing of the lines is guaranteed valid only for the indicated channel although the cursor may be moved over any channel. All or most channels may (especially in the EEG case) have the same gain but other channels (especially in polysomnograms) displayed on the same montage may have differing gains or may be operating with different units.
Changing the gain of the relevant channel (only possible for "EEG" channels) alters the spacing between horizontal channels to correspond.
The classic way of measuring frequency in the EEG is to use a transparent cursor with vertical lines ruled at 1.5 and 3 cm spacing - corresponding to 0.5 and 1.0 seconds at the conventional speed of 3cm/sec.
The time cursor is similar.
Select "Time" from the Cursor choice control
Point somewhere on the display (ideally close to the waveforms to be measured), depress the mouse button and drag to the right to create a Time cursor.
Two vertical lines appear which as you drag sideways become separated in successive jumps corresponding to 0.25, 0.5, 1.0, 2.0 seconds. (you may have to wait a little while for the 'drag' to take effect, Note: the pointer at this stage will be outside the rectangle formed by the horizontal lines.)
Select a convenient spacing and then release the mouse button.
In the 'measurement display area' a message appears
Measure= nn seconds
To measure a section of trace place the pointer between the vertical lines, depress the mouse button (the cursor will 'jump' so that the pointer is at the centre) and drag the whole cursor over the waveform of interest (again the response to the drag may be rather slow).
To create a new cursor simply repeat the procedure anywhere outside the existing cursor lines.
This cursor also behaves like the simple cursor when changing the Xscale but the spacing of the vertical lines is altered to correspond. Note that the spacing of the lines is, of course, valid for any channel.
This cursor function is useful for measuring transient phenomena, for example K-complexes. It can, of course, also be used on a spike, a burst of activity or even a spindle of rhythm.
Select transients from the Cursor choice control
Point to the beginning of the transient and drag to the right as far as the end of the waveform. A horizontal baseline will appear and when the mouse button is released vertical lines show the measured maximum and minimum deflections.
At the top of the screen you can see the maximum upward and downward deflections, the peak-to-peak (maximum) deflection and the length in seconds of the baseline that you have drawn.
This is useful for quantities (e.g. SaO2) which change relatively slowly and are displayed as an absolute value relative to some zero reference.
Simply click on the trace at the time of interest and In the 'measurement display area' a message appears
Channel xx Amp above baseline nn Units
These are: