* units away from 0 and 0.499 towards 0. The smallest unit this returns is "µs"; the largest unit
 * it returns is "s". For values in [-499..499] this returns "  0 µs".
 *
 * The returned string attempts to be column-aligned to 6 characters. For negative and large values
 * the returned string may be longer.
 */
fun formatDuration(ns: Long): String {
  val s =
    when {

222E          ; valid                  ;      ; NV8    # 1.1  CONTOUR INTEGRAL
222F          ; mapped                 ; 222E 222E     # 1.1  SURFACE INTEGRAL
2230          ; mapped                 ; 222E 222E 222E #1.1  VOLUME INTEGRAL
2231..22F1    ; valid                  ;      ; NV8    # 1.1  CLOCKWISE INTEGRAL..DOWN RIGHT DIAGONAL ELLIPSIS