A source moving toward us compresses its spectral lines to shorter wavelengths, a blueshift, the mirror of the redshift case. The same shift ratio Delta lambda / lambda = v / c applies, now with the line pulled toward the blue. The result is exact for an identified line and the low-speed approximation; real measurements fight calibration drift, line blending, and finite instrument resolution, and high speeds need a relativistic correction.
A negative radial speed gives a negative shift ratio. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
The radial speed source carries the sign
The same speed scale uses radial speed -1 meter per second.
v=−1m/s,c=6m/s
The shift ratio is negative
Dividing by the same light speed gives shift ratio -1/6, a blueshift training case.