The ‘IO’ property allows you to set the ‘index origin’ of a generated x-scale. This is 1 by default, but could be 0 which is good for surface filled charts as the auto-ranging of the axis often forces it to include 0, and the surface looks ugly when it does not fill right back to the y-axis

 chSet ('style' 'surface')('io' 0)
 chPlot +\?37½12
 View chClose

Although 1 and 0 are the normal values, IO can take any integer (such as 36967 which is 17th March, 2001) for date labelled axes where the data is daily from a given start date.

 chSet('xt' 1)('io' 36967)('xs' 'date') 
 chPlot ¼23 
 View chClose

This may be helpful when the data is known to have one value per day.