Yes you are absolutelly right.
However, this is only the error caused by the drift on the oscillator.
There is another error, called the Synchronization Error (see http://zone.ni.com/devzone/cda/tut/p/id/3619.
This error is, for the simplest frequency measurement technique:
Er = Fx^2 / (Fk-Fx)
Where:
Fx = unkown frequency (frequency to be measured) GATE. In our case it is 100Khz
Fk = known frequency (frequency used to count in the counter) SOURCE. In our case it is 80Mhz
Therefore:
Er = 125.1564 Hz
So then the total error would be:
Er = Error clock + Error synch = 0.0075Hz + 125.1564Hz
Which is far from my requirements.
Again, I am not sure that the calculations are right and not sure either that you can add up both errors together like that.
