[pstricks] \psxTick error

[David Arnold]

All,

I can't see why the code below is producing this error:

! Missing number, treated as zero.
<to be read again>
                    !
l.15 	\psxTick[linecolor=red](1.5){x_0}

?

\documentclass[12pt]{article}

\usepackage{pst-pdf}
\usepackage{pst-bar}
\usepackage{pstricks-add}
\usepackage{pst-plot}
\usepackage{pst-tree}

\begin{document}

\begin{center}
	\psset{unit=0.125in}
	\begin{pspicture}(-8,-2)(8,0.5)
	\psaxes[arrowscale=1.5,arrows=<->,yAxis=false,labels=none](0,0)(-8,0) 
(8,0)
	\psxTick[linecolor=red](1.5){x_0}
	\uput[270](0,0){$0$}
	\uput[270](7,0){$7$}
	\psdots*[linecolor=red,dotsize=3pt 3](#sa,0)(#sb,0)(#sc,0)(#sd,0)
	\end{pspicture}
\end{center}

\end{document}
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