A dimensionless training ratio compares drift transport with diffusion. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Compare drift and diffusion scales
With speed 2, length 4, and diffusion 2, the ratio is 4.
2⋅4/2=4
The ratio is a training comparison
The value 4 compares drift over a length with diffusion; it is not a random sample.