Texas Instruments TI-83 PLUS - Manual (Page 131)

TI-83 Plus Function Graphing 128
ExprOn, ExprOff
ExprOn and ExprOff determine whether to display the Y= expression
when the trace cursor is active. This format setting also applies to stat
plots.
When ExprOn is selected, the expression is displayed in the top-left
corner of the graph screen.
When ExprOff and CoordOn both are selected, the number in the top-right
corner specifies which function is being traced.