VOPlot is a Java applet. This means you have to have a java virtual machine active within your browser. A common way to get this is to install a plugin, available, e.g., from java.sun.com, or by installing a package like openjdk-?-jre on Debian-derived systems (where ? corresponds to some version).

Also, this HTML page assumes you run a post-Y2k (i.e., at least HTML 4.01) standards-compliant browser. There are plenty of those out there.

If neither applet nor fallback content appears above, your browser's java support is broken.

VOPlot is developed by Persistent Systems in cooperation with VO india. Standalone versions and user guides are available at VO India's VOPlot page.