This frequency-index-compares-to-cutoff lesson turns a signal frequency into a dimensionless filter index by dividing by the cutoff frequency. The 6 Hz over 12 Hz row is exact only for the stated ideal cutoff and signal-frequency inputs. Real filters add component tolerances, loading, parasitics, source and probe calibration limits, finite precision, and measurement uncertainty.
A filter lesson starts by comparing a signal frequency to a cutoff. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Frequency is compared to the cutoff
The signal frequency is 6 hertz and the cutoff is 12 hertz.