Compare the rule with concrete cases
Fictional target and observed counts are nonnegative integers. Target is five marks. At observed seven, target−observed is −2, showing two above target. Additional needed is max(target−observed,0)=0. The fields answer different questions. Marks are abstract teaching units.
| Observed | Signed difference | Additional needed | Interpretation |
|---|---|---|---|
| 3 | 2 | 2 | Two below target |
| 5 | 0 | 0 | At target |
| 7 | −2 | 0 | Two above target |
Work through the distinction
Clamping is correct for additional-needed, but loses the over-target information in signed difference. Label both rather than showing zero without its meaning.
Observed becomes eight. What are the two values?
Show the worked answer
Signed difference is −3; additional needed is zero.
Acceptance wording to adapt
Set signed_difference=target−observed and additional_needed=max(signed_difference,0). Preserve negative signed differences; never describe negative additional-needed quantities.