in⁻¹
per inch
Wavenumberexact by definition
The reciprocal inch is exactly 1/0.0254 m⁻¹, about 39.37 m⁻¹. It appears in American practice as a spatial frequency, most visibly as threads per inch on fasteners and as lines or dots per inch in printing and scanning.
Watch out: Printing resolutions in dpi and screen rulings in lpi are the same dimension but not the same measurement: dpi counts addressable dots, lpi counts halftone screen lines, and a good halftone needs several dots per line in each direction.
| 1 in⁻¹ | 39.370079 m⁻¹ |