Generalized Timing Format

gtf is a utility for calculating VESA GTF modes. Given the desired horizontal and vertical resolutions and refresh rate (in Hz), the parameters for a matching VESA GTF mode are printed out. Two output formats are supported: mode lines suitable for the Xorg xorg.conf(5) file, and mode parameters suitable for the Linux fbset(8) utility.
GTF: Generalized Timing Format (VESA) 

linux/gtf - Department Of Computer ScienceThe GTF provides for computation of interlaced mode timings

* While every precaution has been taken in the preparation
 * of this standard, the Video Electronics Standards Association and
 * its contributors assume no responsibility for errors or omissions,
 * and make no warranties, expressed or implied, of functionality
 * of suitability for any purpose. The sample code contained within
 * this standard may be used without restriction.

 * The GTF EXCEL(TM) SPREADSHEET, a sample (and the definitive)
 * implementation of the GTF Timing Standard, is available at:
 *
 * ftp://ftp.vesa.org/pub/GTF/GTF_V1R1.xls *
 * This program takes a desired resolution and vertical refresh rate,
 * and computes mode timings according to the GTF Timing Standard.
 * These mode timings can then be formatted as an XFree86 modeline
 * or a mode description for use by fbset(8).