void ylab (on_off, labstr)  LABSET.C Level 1
int on_off  = 0 to turn off the y axis string labels (default).
= 1 to turn on the y axis string labels.
char *labstr[ ]  An array of pointers to the individual string labels for each successive tick mark. 
ylab() turns on or off the y axis string label option. When it is on, each string is positioned at a tick mark in the same 
way as numerical labels. There must be at least as many string elements in the array as there are y tick marks. You must ensure that the string will fit between the tick marks. See the example BARTEST.C to see how to use string labels.