The command symbolnumber n instructs plotl which predefined symbol to place on data points.
If n is a number from 0 through 9, a graphical symbol will be used according to this chart.
Symbols 0, 1, 2, and 5 can be drawn as filled symbols, rather than simply outlines, by issuing the filledsymbols command.
The default symbolnumber is zero.
The user can define symbols numbered from 10 through 19 as either a text string, or a number. For example,
definesymbol 10 TEXT H2O definesymbol 11 NUMBER 7.7
defines symbol number 10 as the text string "H2O" and symbol number 11 as the number "7.7".
Symbolnumbers 10 through 19 have no default definitions.