LESSON 14.6 — NAT Discipline and Number-Entry Control
A. Standard Map
| Check | When | Pass criterion |
|---|---|---|
| Method lock | Before calc | Formula + givens listed |
| Unit harmonize | Pre-substitute | Single unit system |
| Compute | During | One line per step |
| Magnitude | Post-compute | Order vs options/physics |
| Entry format | Pre-submit | Integer/decimals per field rules |
| Reverse verify | Pre-submit | Back-substitute or boundary check |
B. Why It’s Used
NAT is ~20 questions with no penalty — entry discipline harvests marks competitors lose post-calculation.
C. Mechanism in Words
- Read NAT stem twice — underline asked variable and units required in field.
- Write formula with symbols before numbers.
- Convert all inputs to SI (or exam-standard) consistently.
- Calculate cleanly; box intermediate if multi-step.
- Magnitude check against options or physical bounds (U-value, PCU, time never negative).
- Entry protocol: no units in box unless instructed; watch rounding; submit only after reverse check.
D. Core Concept Explanations
D1. NAT Failure Modes (Method Right, Entry Wrong)
Wrong decimal place, wrong unit in field, rounded too early, sign error, entered formula constant not final value.
D2. Precision and Rounding Policy
Keep full precision until final step; round only per field rule (often 2 decimals or integer).
D3. Unit Checks and Dimension Sanity Checks
Use dimensional analysis: PCU dimensionless; U in W/m²K; time in consistent hours/days.
D4. Reverse Verification Before Submit
Plug answer back — e.g., FAR × plot = GFA check; TE within [O,P] bounds.
D5. Time Control Under NAT Pressure
Cap per NAT: 3–4 min standard; flag at 6 min; never exceed 8 min in mock without skip rule.
E. Worked Workflows and Practice Drills
Drill 1 — U-value assembly
Wall: brick 230 mm λ=0.8, plaster 20 mm λ=0.5. R_total = 0.23/0.8 + 0.02/0.5 = 0.2875 + 0.04 = 0.3275 m²K/W. U = 1/0.3275 = 3.05 W/m²K.
Checklist: ✓ units ✓ magnitude (U typically 1–5) ✓ entry 3.05 not 0.3275 (reciprocal trap).
Drill 2 — PCU flow
400 cars (PCU=1), 800 two-wheelers (0.5) → PCU = 400+400 = 800.
Checklist: ✓ didn’t use ECS ✓ dimensionless ✓ integer entry.
F. Design Criteria
| Element | Fact |
|---|---|
| NAT penalty | None |
| Typical cap | 3–4 min target |
Code Comparisons
| MCQ guess | NAT blank |
|---|---|
| −⅓ risk | Zero loss |
G. Application Zones
Every NAT in mock uses 6-step checklist; error log tags A vs entry failure.
H. Common Confusions
- NAT allows guessing — never; blank beats wrong if time expired.
- R vs U reciprocal swapped at entry.
- Early rounding in multi-step (PERT variance chains).
- Units in entry field when portal expects bare number.
- Skipping magnitude check because “calculation long”.
- Same protocol as MCQ elimination.
I. Compare & Contrast
Application tier skill ≠ entry discipline — both required.
J. Memory Hooks
Method → unit → magnitude → entry → reverse · Never guess NAT
K. Revision Ladder
Complete 2 Section D drills under time; log any entry error separately in L14.4.
L. Exam Traps
| Trap | Correction |
|---|---|
| Reciprocal entry | Label U vs R before box |
| PCU/ECS mix | Separate formulas |
| Percent vs decimal | ×100 check |
| Hours vs days PERT | Convert first |
| MSQ logic on NAT | Full calc only |
| 8+ min NAT | Skip flag return |
| Copy intermediate | Final value only |
| Two decimals required | Round at end |
| Negative impossible | Sign check |
| No reverse verify | Mandatory step 6 |
M. Answer-Writing Cues
NAT scratch: “Asked=[ ] Units=[ ] Formula=[ ] → substitute → magnitude → entry → reverse.”
N. PYQ Integration (2007–2026 verified)
| NAT family | Common entry trap |
|---|---|
| Thermal U-value | Reciprocal |
| PERT TE | Decimal vs fraction |
| FAR/GFA | Unit m² consistency |
| Demographics | % vs ratio |
O. Mini-Check — Lesson 14.6 (5 Questions)
Q1 (MCQ): Largest silent NAT loss? Answer: (b) Method correct, entry wrong
Q2 (MCQ): U=1/R. Computed R=0.33, entered 0.33 instead of 3.03. Class? Answer: (a) Reciprocal entry trap
Q3 (MCQ): When to round? Answer: (c) Final step per field rule
Q4 (MCQ): NAT time cap in mock? Answer: (b) Flag at 6 min, skip rule at 8
Q5 (MSQ): Pre-submit checklist? (a) Unit harmonize (b) Guess if stuck (c) Magnitude check (d) Reverse verify (e) Units inside field always
Answer: (a), (c), (d)