Adds one single numerical pair to the graph, but
only if there is only one series of data; this
method should be used after 'addEmptySeries'
to ensure no messing up of data that does not belong together
Adds a number of numerical (x,y) pairs to the graph (scatterplot) , but
only if the number is the same as the number of existing
series; this method should be used after 'addEmptySeries'
to ensure no messing up of data that does not belong together