Shear rate is the speed difference across a gap divided by the gap width, so a wider gap with the same speed jump gives a lower rate. With speed difference 8 m/s across gap 4 m, the shear rate is 8/4 = 2 reciprocal seconds exactly for the stated toy flow model; real viscoelastic flow can have nonuniform shear, wall slip, geometry limits, instrument calibration, and measurement uncertainty.
A uniform training shear rate is checked from speed difference and gap. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Use speed difference and gap height
The speed difference is 8 m/s across a gap of 4 m.