Use 'spot on' to affirm someone's correct action or thought.

Confirming Correctness

It's often used colloquially to express admiration for someone's correct thinking or doing.

Colloquial Compliment

Avoid using 'spot on' for precise numerical accuracy. It's more for general correctness.

Use 'spot on' to compliment someone's perfect timing or punctuality.

It's handy for emphasizing the start or end time of events and how timely they were.

Indicate promptness in action with 'spot on'. It means no delay was involved.