SetPrecisionY — Set precision for numeric formated Y tick labels
$plot->SetPrecisionY($prec)
SetPrecisionY sets the desired numeric precision
for Y tick and data labels, and also enables 'data' mode formatting
of those labels with SetYLabelType.
Setting numeric precision with this function automatically enables 'data'
mode formatting as if SetYLabelType('data') was called.
The default is to format numbers with 1 decimal position, but only if 'data' mode formatting is selected.
This function applies to Y tick labels, and also to the Y data labels available with bar charts.