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Commerce · III.09 · MMXXVI · daylight

La Bourse  /  Volume III  /  Nº III.09  /  Workbook — the student

WORKBOOK — THE STUDENT

Chapter III.09 · Digital Settlement Without Extraction

A term of practice. Applied to a life, not a firm.

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WHY THIS WORKBOOK IS DIFFERENT

Most of what you will read about payments is written for people who run shops. You probably do not run a shop. You are on the other side of the counter, and the chapter's central finding is about you: the acceptance fee is in the shelf price, so you pay it whichever way you pay.

At £600 a month of card spending and an all-card fee rate of 1.57 per cent, the embedded fee is £9.42 a month and £113.04 a year. That is not a number you can avoid by using cash — it is in the price either way. What you can do is see it, understand who it goes to, and be one of the people who can explain it in a room, which turns out to be rarer and more useful than it sounds.

This term you will do four things: learn to read a payment as a system, learn to compute the two ratios that matter, run one small field study you can actually do, and produce one piece of work that would be useful to somebody who is not you.

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PART ONE — DISCOVERY

Weeks 1–4: learn to see the rail

Exercise 1.1 — The receipt audit. Keep every receipt for two weeks. For each one write down the payment method, the amount, and — this is the part that teaches — whether the price would have been different by any other method. In almost every case it would not. That uniform price is the mechanism from Brief 6: the fee is pooled across all payers and the rewards go to some of them.

Exercise 1.2 — Find a differentiated price. Now hunt for the exceptions: a card surcharge, a cash discount, a "card minimum" sign, a bank transfer discount on a large purchase. Photograph three. For each, estimate what the merchant is trying to recover. A "card minimum" sign is almost always a fixed-fee problem, not a percentage problem — and being able to tell those two apart is half of this chapter.

Exercise 1.3 — The four rails, in your own life. Make a table of every way you have moved money in the last year: card, instant bank transfer, cash, a wallet, possibly a ledger. For each, write the finality from Brief 4 — 60 minutes probabilistic, 12.8 minutes deterministic, seconds and irrevocable, or immediate and physical — and then write what you actually felt about the wait. The gap between the engineering answer and the felt answer is worth a paragraph.

Exercise 1.4 — One published figure. Go and find one primary payment statistic yourself, from a central bank, a national operator or a statistics office. Not a news article about it: the source. Write down the figure, the denominator, and the date. This is the single most transferable skill in the whole volume, and you will do it badly the first time.

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PART TWO — THE ARITHMETIC

Weeks 5–8: compute before you argue

Exercise 2.1 — The wedge, in three lines. Write out the three Brazilian figures and the two ratios between them:

  central bank settlement charge      0.000226 % of value
  merchant cost on Pix                0.22 %              = 975 x
  card merchant discount rate         2.2 %               = 9,748 x

Then write one paragraph arguing the strongest possible case that the 2.2 per cent is justified. Do it properly. A student who can only argue one side of this has not learned it.

Exercise 2.2 — Ad valorem against flat. Take a representative card rate of 1.8 per cent and a flat fee of €0.29. Compute the fee on a €40 basket and on a €4,000 basket under each. You should get €0.72 and €72.00 against €0.29 and €0.29 — a 100-times spread against no spread at all, and 248.3 times difference on the large basket. Then find the basket size at which the two are equal, and say what that number means for who each pricing model favours.

Exercise 2.3 — The energy question, done fairly. Compute Bitcoin's implied transactions per year from 138 TWh and 1,100 kWh per transaction. You should get 125.5 million, or 3.98 a second. Compare with Pix's 2,530 a second — a factor of 636.

Now do the harder half. Write down, in your own words, why 1,100 kWh per transaction is an average rather than a marginal cost, and why the security budget — $16.43 billion a year of issuance, $130.92 per transaction — is the figure that does not have that problem. A student who quotes the first number without the second is doing advocacy.

Exercise 2.4 — The adoption arithmetic. Compute share gained per year for the three rails: 11.1 per cent over seventeen years, 83.4 over nine, 54.7 over five. You should get 0.65, 9.27 and 10.94 points a year. Then write one sentence naming the mechanism behind each, and one sentence on why comparing them is only an order-of-magnitude exercise — the three denominators are not the same.

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PART THREE — DREAM AND DESIGN

Weeks 9–12: build something small

Exercise 3.1 — The field study. Visit ten small independent merchants near where you live. Ask each one three questions, in this order, and write the answers verbatim:

1. What does it cost you to take a card?
2. Is there a payment method you would rather people used?
3. What would have to change for you to ask for it?

You will find that many cannot answer the first question precisely. That is the finding, not a failure of your method: a fee that nobody can state is a fee nobody is negotiating.

Exercise 3.2 — The one-page brief. Write a single page for one of those ten merchants. Their volume, their current fee, the fee on the cheapest rail available in your country, the saving, and the saving as a share of their net profit if they will tell you the margin. Use the Brief 10 frame: at a 4.0 per cent margin the saving is 49.5 per cent of net profit; at 3 per cent it is 66.0 per cent; below 1.98 per cent the fee exceeds the whole profit.

Give it to them. Actually give it to them. The exercise is not finished until a real person has held it.

Exercise 3.3 — Design the acceptance mechanism. Your country has, or will have, an instant rail. Design the acceptance answer for it, choosing one of the four from the chapter: mandate, subsidy, bank-owned flat-fee scheme, or nothing. Cost your choice. If you choose a subsidy, say at what rate and for how long — India paid 0.15 per cent of value on small merchant transactions, spent 8,730 crore over four years, and still ended zero MDR on 15 October 2026. If you choose a mandate, say who it binds and what they will say about it.

Exercise 3.4 — The counter-case, written properly. Write eight hundred words arguing that the public-rail case in this chapter is overstated. You have real material to work with and you should use all of it: that the 0.22 per cent Brazilian merchant cost is 975 times the central bank's own settlement charge, which means almost all of it is genuine operating work and a further large reduction may not exist; that instant irrevocable payments remove the chargeback protection a consumer currently enjoys without charge; that a state-operated rail concentrates a systemic dependency in one institution; and that India's zero-fee regime lasted six years before a 0.4 per cent fee returned above ₹2,000 on 15 October 2026.

A student who cannot write this essay has read the chapter as an advertisement.

Exercise 3.5 — The denominator hunt. Take the three adoption shares — 11.1 per cent of all United Kingdom payments, 54.7 per cent of Brazilian retail payment transactions, 83.4 per cent of the Indian payments ecosystem by volume — and write down precisely what each denominator contains and excludes. Then say, in one sentence each, what the comparison can honestly support and what it cannot. This exercise takes an hour and it will improve every piece of quantitative writing you do afterwards.

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THE FOUR MISTAKES THIS CHAPTER INVITES

Every chapter makes a characteristic error easy. Here are this one's, named so you can avoid them.

Quoting 1,100 kWh without the caveat. It is an average across blocks, not the marginal cost of one more payment. Quote the security budget beside it — $16.43 billion a year of issuance, $130.92 per transaction — or do not quote either.

Treating 0.22 per cent as a floor. It is not a target achievable by wishing. It is the observed all-in cost of a working payment business — fraud, disputes, onboarding, support — on a rail with no rent in it, and it is 975 times the settlement charge underneath it for exactly that reason.

Comparing shares across denominators without saying so. See Exercise 3.5.

Assuming free is a property rather than a phase. Zero merchant discount rate in India ran from January 2020 and ended on 15 October 2026, after the state had spent 8,730 crore, about $992 million, against a running cost estimated at 20,000 crore a year. Somebody always pays for acceptance. The interesting question is only who, and whether it is visible.

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PART FOUR — DESTINY AND DELIGHT

Weeks 13–16: make it hold, and notice it

Exercise 4.1 — The sunset clause. Write the paragraph that would stop the merchant mutual's 0.10 per cent levy becoming interchange in a decade. One paragraph, legal-sounding, specific about who decides and when. Then write the paragraph a well-meaning person would use, ten years later, to keep the levy — and notice that you find the second one easier. That is the whole of Destiny in one exercise.

Exercise 4.2 — The dispute question. The chapter names a failure that most advocates skip: instant irrevocable payments have no chargeback, and the card rail's expensive 2.2 per cent buys a dispute process. Write six hundred words on where the dispute function should live on a cheap rail, and who pays for it. There is no settled answer. Say which answer you would defend.

Exercise 4.3 — Notice the delight. Pay somebody instantly — a friend, a market stall, a small trader — and watch their face when it lands. Write four sentences about it, without using the words efficient, frictionless or seamless. The chapter's claim is that a payment which costs almost nothing stops being an event and becomes a gesture. Test the claim.

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THE TERM PROJECT

One piece of work, carried the whole way

Build the payment cost profile of one small organisation, end to end.

Choose a shop, a café, a market trader, a charity, a student society — anything with real payment volume that will talk to you. Then produce:

1. The fee decomposition. Their statement, separated into interchange, scheme fees and acquirer margin. Most statements resist this. Say where yours became guesswork, and how much of the total the guesswork covers.
2. The two ratios. Fee as a share of revenue, and fee as a share of net profit. The second is the one that will surprise them.
3. The migration model. What happens at 30, 50 and 100 per cent migration to the cheapest available rail. Use the Brief 10 frame. State your assumptions on a separate line, as assumptions.
4. The acceptance answer. What would actually have to happen for their customers to use the cheaper rail. This is the honest part and it is usually the hardest.
5. One page they can keep. No jargon. One number in bold.

What makes it good rather than complete. A project that concludes "they should switch" is a homework exercise. A project that concludes "they cannot switch, and here is precisely what is stopping them, and here is what it would cost to remove it" is a piece of research, and it is the one the chapter is actually asking for.

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SELF-ASSESSMENT

Mark yourself honestly against these. Nobody else will see it.

The one that matters most is the last. This chapter has an obvious side, and a student who can only argue that side is not yet doing economics.

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CARRYING IT FORWARD

Three things worth keeping past this term.

The habit of finding the denominator. Every share in this chapter — 11.1 per cent, 54.7 per cent, 83.4 per cent — sits on a different denominator, and saying so is what makes the comparison honest rather than promotional. You will meet this everywhere.

The instinct to price the objection. The chapter's negative is not "this might not work". It is: a rail without a margin has no salesforce, here is what three countries paid to fix that, and here is the country that did not and what it got. Price the objection or you have not made it.

The two ratios. Cost as a share of value moved, and cost as a share of net profit. They travel far beyond payments, and between them they will let you say something useful about almost any fee you ever meet.

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APPRECIATIVE QUESTIONS FOR YOUR SEMINAR

1. Where have you seen a price that was clearly not a cost, and what made it visible to you?
2. Which of the ten merchants you visited gave the most interesting answer, and what made the question work?
3. If your university moved all of its supplier payments to the cheapest available rail, what would you want the saving spent on?
4. What is the strongest argument for interchange that anyone in this room can make — and can the person who believes it least make it best?