How can I get correct display scales?

Use `xdpyinfo' (a standard X client that is provided as part of the X core distribution) to check several server parameters. (As with virtually all X clients, it doesn't matter which machine you find `xdpyinfo' on; it will query your server from wherever it is run.) `xdpyinfo' will report the version and release numbers of your server; you should have version 11, release 3 or later. It will also report the screen size in pixels and the resolution in pixels per inch. Take a minute to verify the screen resolution by direct measurement of the screen with a ruler. If the resolution reported by `xdpyinfo' is incorrect, WAVE will not be able to draw waveforms at properly calibrated scales. The sample X11 servers from MIT and the X Consortium, and the XFree86 project's X11 servers, all support a `-dpi' option, which allows you to specify the correct screen resolution at the time the server is started; read the man page for X or Xserver for details. (If your server does not support this feature, WAVE can be given a similar `-dpi' option.)

You can also double-check your display calibration using WAVE itself. Run WAVE , enable the grid display, and set the display scales to their default values (25 mm/sec, 10 mm/mV). (Click on \ovalbox{\rule[-.3mm]{0cm}{2.5mm}\small\sf ~View...~} to pop up the controls for the grid and the display scales; remember that any adjustments you make become effective only after you click on \ovalbox{\rule[-.3mm]{0cm}{2.5mm}\small\sf ~Redraw~} within the View window.) The grid intervals should measure exactly 5 mm in each direction. If they are too small, use a larger value for the `-dpi' specification; if the grid lines are more than 5 mm apart, decrease the `-dpi' values.

George B. Moody (george@mit.edu)
2014-03-13