Does the next stage understand what this number means?
Create an input contract with units and a missing-data policy. Supply at least one valid and two invalid cases.
Require a finite number, the exact unit and a non-empty source; reject rather than silently convert.
Cut these cards apart. Use the original example first, then let a partner supply a changed case. Keep sealed/final cards with the teacher until the learner commits a rule.
Value: 20
Unit: C
Source: sensor-a
My prediction and reason:
Value: 68
Unit: F
Source: sensor-b
My prediction and reason:
Value:
Unit: C
Source: missing
My prediction and reason:
Value: hot
Unit: C
Source: text
My prediction and reason:
A contract prevents these declared errors only; acceptable conversions must be designed explicitly.