Drawing vs Bill: The Money Link

Every rupee in a construction bill claims descent from a drawing. Cable metres descend from a schedule, concrete cubes from framing plans, saleable area from area statements. When the bill and the drawing agree, payment is boring — which is what payment should be. When they disagree and nobody checks, money leaks in whichever direction carelessness points. This lesson gives you the third face of the discrepancy eye: tracing a billed quantity back to the drawing that gave birth to it.

If you have taken our QS course, this is where the two courses shake hands: the RA-bill machinery lives at /learn/planning-billing-control/ra-bills-progress-billing and the measurement book at /learn/planning-billing-control/measurement-book. Here you learn the drawing side of that handshake.

Where a billed quantity is born

The chain has five links: drawing (at a specific revision) → takeoff quantity → BOQ item → measurement book entry → RA bill line. A change at any link must travel the whole chain or the chain lies. The two failure modes you will meet constantly on Indian sites:

• The bill outruns the drawing — quantities claimed that the current revision cannot support.
• The drawing outruns the bill — a revision added scope that nobody claimed, and the contractor silently eats it.

Both are found the same way: put the drawing's own numbers beside the bill's.

Case 1: the cable schedule that audits itself

Electrical drawings often carry their quantities openly, in selection tables. This one is from Project A's cable schedule.

How to read this

1. Read row 1 left to right: CSS (1600 kVA) to Main LT Panel, 0.415 kV system, demand load 1440, load current 2226 A.
2. Verify the current: 16,00,000 / (1.732 x 415) = 2,226 A — the feeder is sized on the transformer's full 1600 kVA rating, not the 1440 connected load.
3. See how current becomes copper — here aluminium: 3.5C x 300 sqmm AL XLPE in 7 parallel runs, route length 35 m.
4. Reproduce the total: 7 runs x 35 m = 245 m in the Total Length column. Check the pattern on the other rows: 2 x 47 = 94, 5 x 46 = 230, 1 x 55 = 55.
5. Note the header slip — % Comulative Voltage drop — another live-project spelling artefact. The data beside it is what you verify.
6. Bill-check habit: any RA-bill claim for this feeder must bridge from 245 m plus named allowances; an unexplained gap is a written query.

Read the transformer feeder row end to end: from the CSS (1600 kVA) to the Main LT Panel at 0.415 kV, demand load 1440, load current 2226 A, aluminium XLPE, route length 35 m, cable size 3.5C x 300 sqmm AL, 7 runs, and total cable length 245 m.

Two verifications, both worth doing with a calculator in front of the bill:

Check 1 — the current is honest. 1600 kVA at 415 V three-phase gives 16,00,000 / (1.732 x 415) = 2,226 A. The designer sized the feeder for the transformer's full rating, not the 1440 connected load — which is why 1440 in the load column sits beside 2226 in the current column. (Try the wrong math: 1440 kVA gives 2,003 A. Now you know which number the designer used and why.)

Check 2 — the total length is just multiplication. Runs x route length: 7 x 35 = 245 m. The other rows obey the same law: 2 x 47 = 94, 5 x 46 = 230, 1 x 55 = 55. The schedule audits itself — every total-length cell is reproducible from two cells to its left.

Now put a bill beside it

Suppose the electrical contractor's RA bill claims 320 m of 3.5C x 300 sqmm AL for the transformer feeder. Build the reconciliation before the meeting, not during it:

At an indicative mid-2026 dealer range of Rs. 1,100-1,400 per metre for branded 3.5C x 300 sqmm aluminium armoured XLPE (supply only; always use current quotations), 68 unexplained metres is roughly Rs. 75,000-95,000 on a single bill line — found by one multiplication and one comparison. The query is not an accusation: perhaps the route genuinely changed. Then the answer is a revised drawing or a measured route in the MB — either of which repairs the chain. What you never do is certify the 320 with the 245 sitting unexamined on the drawing.

Case 2: the area statement that does not add up

Areas are quantities too — the most expensive ones on the project, because saleable and FSI calculations ride on them. This is Project A's sanction-set area statement.

How to read this

1. Learn the row logic first: BLOCK AREA − LIFT/SHAFT = GROSS BUILT UP. Test it on Basement 2: 2144.90 − 14.52 = 2130.38.
2. Note the repetition trick: floors 1 through 9 repeat 1463.59 / 17.36 / 1446.23 — typical floors mean typical rows, so one wrong master value would repeat nine times.
3. Spot the 7th-floor exception: a 150.20 refuge area appears, and B.A.R. achieved drops to 1274.59 while other floors show 1424.79.
4. Re-add the lift/shaft column: 14.52 + 179.25 + 99.26 + 19.62 + nine 17.36 rows = 468.89 — but the printed TOTAL reads 471.07.
5. Cross-prove it: block total 20,446.74 minus gross total 19,977.85 = 468.89. Two verified columns outvote one printed total; the 2.18 sq.mt slip is real.
6. Close out like a professional: an RFI quoting both numbers — never a silent correction, never a shrug.

The table's own logic is: block area − lift/shaft = gross built-up, floor by floor. Spot-check it: Basement 2, 2144.90 − 14.52 = 2130.38. First floor, 1463.59 − 17.36 = 1446.23. The rows are clean.

Now audit the TOTAL row the way you audited the cable table — by recomputing it:

And here is the elegant cross-proof: since block and gross totals both check out, the lift/shaft total must equal their difference — 20,446.74 − 19,977.85 = 468.89. The printed 471.07 disagrees with the table's own other columns. Somewhere in this sheet's history a row was revised and the column total was not — a data slip, the tabular cousin of the title-block mislabel from Lesson 1.

Is 2.18 sq.mt worth an RFI? Convert it: 2.18 sq.mt = about 23.5 sq.ft. In a metro project selling at, say, Rs. 9,000 per sq.ft, that is roughly Rs. 2.1 lakh of area whose paperwork is internally inconsistent — in a statutory table that FSI achievement and RERA declarations reference. The RFI costs one paragraph. More importantly, the habit that found it — never trust a printed total; re-add at least one column of every quantity table you rely on — is the same habit that catches the lakhs-sized version in a BOQ summary or a final bill abstract.

The reconciliation habit for RA bills

Before certifying (or submitting) any bill line that descends from a drawing:

1. Fix the revision. Which issue of the sheet supports this quantity? Write it in the MB narration — "as per drg. [number] rev [x]". Module 5 taught you why: a superseded sheet supports nothing.
2. Reproduce the drawing's own number. Runs x route, riser count x height, block − shaft. Drawings constantly carry self-auditing arithmetic; use it.
3. Bridge to the billed number explicitly. Allowances (wastage, laps, terminations) are legitimate but must be named, percentaged and consistent with the contract — not smuggled inside a bigger number.
4. Query deltas in writing, with both numbers quoted. Same no-blame format as every RFI in this module.

Common mistakes

• Billing or certifying from a superseded revision — the quantity may be perfect arithmetic on a sheet that no longer governs.
• Re-measuring what the drawing already totals — walking the cable route with a wheel when the schedule's route-length column exists is fine as a check, but your query must cite the drawing's number, because that is the number the consultant will defend.
• Trusting totals because they are printed in bold. Totals rows are the least-verified cells in any table — they are computed once and rarely re-checked after row edits.
• Rounding areas casually. 2.18 sq.mt looks trivial until multiplied by a saleable rate or an FSI ratio.
• Treating the query as a confrontation. Most deltas have innocent explanations; the written query simply forces the explanation to exist.

The capstone is next: no new theory, just drawings — including a formwork plan and a raft reinforcement sheet from Project B — and a series of find-the-discrepancy exercises to run your trained eye at full speed.