Update src/dls_bluesky_core/core/maths.py

Co-authored-by: Tom C (DLS) <101418278+coretl@users.noreply.github.com>

src/dls_bluesky_core/core/maths.py

@@ -46,5 +46,5 @@ def in_micros(t: float) -> int:
  t (int): A time in microseconds, rounded up to the nearest whole microsecond,
  """
  if t < 0:
- raise ValueError
+ raise ValueError(f"Expected a positive time in seconds, got {t!r}")
  return int(np.ceil(t * 1e6))