well, usually what is see is that the y-axis has to be the same unit for all series (for example, diastolic blood pressure, systolic blood pressure, mean arterial pressure in mmHg vs. time in minutes).
but since it's your report, if you represent it in a stunning way that fully captures everything in one graph, i don't see why not. xD
but don't take my word for it, though.
what exactly are you trying to graph? o.o
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Primum non nocere
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