This is the xdatplot Units dialog:
The idea behind this dialog is as follows: You have some kind of detector, e.g. a thermistor or an electrode, that measures a quantity whose units have a name, for instance degrees centigrade or picoamperes. This unit should be set in the V Units field. The detector is connected to an amplifier or signal conditioner, which has an output in volts that is proportional to what the detector sees. The constant of proportionality goes in the Gain field. For instance, in the example shown, a patch clamp amplifier was set to produce a voltage of 0.002 V for every pA it measured. Finally, you have an analog to digital convertor that digitizes the voltages and stores them in a data file. These numbers are proportional to the input voltage, and this constant of proportionality (the voltage represented by each increment in the ADC) is the V Multiplier. For instance, in the example, the number 245 in the datafile would represent 0.000610352 * 245 = 0.150 V at the ADC, or 0.000610352 * 245 / 0.002 = 75 pA at the electrode.
Normally your data acquisition software will know what the V Multiplier is and will store it in your data file. xdatplot will then set it automatically. You aren't allowed to change it. If you want to change the Multiplier, you must click the toggle button next to the text field.
There is some flexibility in the way you set these units. For instance, in the example you might prefer to set the units to nA, in which case the Gain should be changed to 2.
The horizontal axis works similiarly. Normally your data are sampled in time, the sampling frequency will be stored in your data file, and the multiplier, i.e. the factor by which raw time units (the number of points) needs to be multiplied to get real time units, will be set by xdatplot as the reciprocal of the clock frequency. As with the V scale, you can use Gain to change units. For instance, you might set Gain to 60 and Units to min. It is also possible, of course, that your data are sampled in some other dimension than time. For instance, they might represent light intensity at an array of points in space. You can set the Units, Gain, and Multiplier so that they horizontal axis of the plot window displays correctly.
The units settings influence many of the other actions that xdatplot takes. For instance, peak heights and half-widths (see Peaks) and many filter parameters are measured in the units controlled by this dialog.
Default units can be set with the tUnits, tGain, tMultiplier, and vUnits, vGain, and vMultiplier resources. See Customizing (X resources).
Leon Avery (leon@eatworms.swmed.edu)