[mikemaccana]

Stacked on #22. Follows quicknode/solana-program-examples#121, which is merged.

The rename

cumulative_borrow_rate_index described neither a rate nor what the number is for. A rate is per unit of time; this value is the accumulated product of 1 + rate_per_slot × elapsed_slots, which is an accumulation factor — as its own doc comment already said. The companion repository renamed it, and this updates the book to match, so no prose names a field that does not exist.

From	To
cumulative_borrow_rate_index	borrow_accumulation_factor
borrowed_amount_scaled	borrowed_principal

Changed:

• solana-building-blocks/time.md — the formula block is now new factor = old factor × (1 + rate per slot × elapsed slots).
• financial-programming-concepts-in-solana/the-arithmetic-of-money.md — this chapter owns the concept, so it carries the fullest definition. Heading is now "One Accumulation Factor Compounds Interest for Every Borrower".
• building-financial-products-in-solana/lending.md — the account model and invariants sections.
• appendices/glossary.md — the entry is retitled borrow accumulation factor and moved alphabetically into the B's.
• Five lending figures that showed either identifier.

The perpetual futures venue's cumulative_funding is left alone. It is an additive accumulator (funding owed is size × (current − entry)), not a multiplicative factor, so "factor" would be wrong there.

Two clarity fixes carried along

• The fundraiser's two handler conditions are now a two-item bulleted list. They are a comparison a reader wants to hold side by side. The prose after them keeps the reason both come from one expression.
• The What You Learnt summary said four questions decide the clock; the decision tree asks three and defaults on three noes.

Verification

npm run lint clean, node scripts/check-figure-geometry.mjs clean across 72 figures, npm run build-pdf at 175 pages. Every renamed identifier greps to a real field in the companion repository at main.

---

Generated by Claude Code