A viscosity scan shows the above, boundary, and below cases for the same threshold. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Low viscosity leaves the ratio above the boundary
Density, speed, and length stay fixed. Viscosity 1 Pa*s gives Reynolds number 24, which is above the threshold 12.
Re=μρvL=24
The middle viscosity sits exactly on the boundary
Viscosity 2 Pa*s gives Reynolds number 12. The helper classifies equality as at-or-above the threshold, so the boundary case is not hand-waved.
Re=μρvL=12
High viscosity pulls the ratio below the boundary
Viscosity 4 Pa*s gives Reynolds number 6. The comparison is a dimensionless training gate, not a full microfluidic stability model.