The costs with no line item.

There are always two prices, not one

01.03.03 showed you this and it is worth restating as a cost. At any moment there is a highest price somebody is willing to buy at, and a lowest price somebody is willing to sell at. They are never the same number.

Say Bharat Foods sits at ₹500 with a 50-paise spread: buyers at ₹499.75, sellers at ₹500.25. If you want in immediately you pay ₹500.25. If you want out immediately you receive ₹499.75.

So the moment you buy, you are down 25 paise a share against the middle — before the price has moved at all. Buy and sell straight back and the round trip costs the whole 50 paise: on ten shares, ₹5.

Set that beside 01.09.01. Every statutory charge on the ₹5,000 purchase came to ₹5.94. The spread on the round trip is comparable to all of them together, and it appears on no document.

What you are paying it for

This is the part that gets taught wrongly, so CANON is strict about it: the spread is not a fee anybody charges you. There is no counter where it is collected.

It is the price of immediacy. Somebody is willing to take the other side of your order right now, carrying the risk of holding what you sold or selling what you bought, and the spread is what they are paid for standing there. 01.03.03 called them market makers.

You can refuse to pay it. Place a limit order at ₹499.75 and wait, and you cross nothing — but now you may not get filled, and if the price runs away you have paid something worse than the spread for the privilege of saving it.

That trade-off is the whole of it. Immediacy costs the spread. Patience costs the risk of not trading.

The spread is not a fee you are charged. It is a fee you pay anyway.

Slippage: when the price moves while your order is filling

The second invisible cost only appears when your order is large relative to what is resting in the book, and it is easiest to see in the order book from 01.04.01.

Four buy orders were waiting: 200 shares at ₹501, then 500 at ₹500, then your own 10 at ₹500, then 800 at ₹499.

Now suppose somebody sells 800 shares at market. They see ₹501 at the top of the book. They do not get ₹501 for 800 shares — they get ₹501 for the first 200, ₹500 for the next 510, and ₹499 for the last 90, because that is all the demand there is.

Why this is not the broker's fault

Nothing went wrong in that example. The order was routed correctly, the engine matched it by price and time exactly as 01.04.01 described, and every fill was the best price available at the moment it happened.

Slippage is what a market order is for. You asked for certainty of execution and accepted uncertainty of price, which is the bargain 02.03.01 will state formally. The book simply did not have 800 shares at one price.

It follows that slippage is a function of two things you can observe before you trade: the size of your order, and the depth of the book you are trading into. Ten shares of a heavily traded company will barely move it. Eight hundred shares of a thin one can cost far more than ₹690.

They get worse together, and at the worst moment

The uncomfortable part is that these two costs are correlated, and correlated with everything else going wrong.

When a market falls hard, market makers widen their spreads or step back entirely, because the risk of standing in the middle has gone up. At the same moment, resting orders thin out, so the book a market order walks into is shallower. And at that same moment is when most people want to sell.

So the cost of getting out is highest exactly when the desire to get out is strongest. 02.04.04 has a whole lesson on liquidity disappearing, and Part 21 builds position sizing around the fact.

The practical version for now is short. Small, patient orders in liquid shares pay almost nothing. Large, urgent orders in thin ones pay a great deal — and neither cost will ever appear on a statement you can point at.