Why do the command cvt and gtf give different frequency values

I am trying to setup a xrandr mode line for a X display but in attempting to find the appropriate parameters, I note there are two different calculation programs (see below). Why the difference in values? Which set should I use for a NON-CRT display? $ gtf 1600 1200 60 # 1600x1200 @ 60.00 Hz (GTF) hsync: 74.52 kHz; pclk: 160.96 MHz Modeline "1600x1200_60.00" 160.96 1600 1704 1880 2160 1200 1201 1204 1242 -HSync +Vsync $ cvt 1600 1200 60 # 1600x1200 59.87 Hz (CVT 1.92M3) hsync: 74.54 kHz; pclk: 161.00 MHz Modeline "1600x1200_60.00" 161.00 1600 1712 1880 2160 1200 1203 1207 1245 -hsync +vsync