Horizontal Y draws a vertical line from the left of the graph screen to the right at Y. Horizontal is usually only used to replace a line that stretches the entire length of the graph screen, along with its counterpart Vertical.
Horizontal is affected by the window settings, unlike the Pxl- commands.
One of the fastest ways to make the entire screen black is by drawing horizontal lines from the bottom of the screen to the top.
:For(A,Ymin,Ymax,ΔY :Horizontal A :End
If working with TI 84+C version calculators, the Horizontal command takes an additional color argument, as shown below: