Why is the reported VCO frequency for my PLL not the exact value I expect when calculating it using the counter settings?

Description The VCO frequency is calculated using the equations on the PLL support page at: http://www.altera.com/support/devices/pll_clock/basics/pll-basics.html. Quartus® II may report the VCO frequency to be slightly different than you would calculate using these equations due to rounding errors. The VCO frequency is shown in the Quartus II compilation report file in the Fitter - Resource Section - PLL Summary. For those concerned with PLL accuracy, you can be assured that the output frequency will be directly related to the input frequency and the counter settings and that the report in Quartus II could be slightly off due to rounding errors. Use the M, N, and post scale counter values as shown in the PLL summary and PLL usage reports to calculate the exact frequency value of your PLL generated clocks.