Spreadsheets, Networks, and Ratios: APR to Subnets to RAID

Work numbers hide in three dialects: spreadsheet finance, packet-and-file ops, and “other” utilities people bookmark next to Excel. APR is not IRR. Churn is not CPM. A UUID is not a subnet. RAID capacity is not password entropy. This hub is the work-numbers silo on pancalc. For compound interest, savings goals, and 401(k) personal cash, use compound interest vs savings goal instead of this page. Education only — not investing, lending, or security assurance.

If you only remember one sentence: name whether you are pricing a loan, valuing a project, running a shop or SaaS, addressing a network, or sizing storage/secrets.

Loans and projects (not your vacation savings)

The APR calculator is about a borrowing rate presentation. Jurisdictions define what must be inside APR. It is adjacent to consumer loans in the housing silo (amortization, PITI) but it is not a monthly payment schedule by itself.

NPV discounts a cash-flow list at a stated rate. Sign convention (outflows negative) matters. NPV is not “profit this year.”

IRR finds r such that NPV = 0. Multiple IRRs exist for unconventional sign patterns. IRR is not APR, not CAGR of a savings account (compound hub), not staking APY.

Worked: a project −1000 then +600, +600. IRR is a rate; NPV at 10% is a currency amount. Report both with the rate you assumed. Do not paste them into a CPM ad tool.

Shops, books, calendars

Margin calculator — confirm whether the page is on sales or cost (markup lives in the percent-math silo as markup/discount). Margin 25% is not markup 25% on cost.

GMROI = gross margin dollars / average inventory (teaching form). A luxury SKU can win margin and lose GMROI if it sleeps.

Straight-line depreciation is (cost − salvage) / useful life. Tax codes have other schedules. This is book teaching, not a cash outflow.

Fiscal week maps a date to a retailer-style week index. It is not “today’s date” (household hub) and not a countdown. ISO week vs 4-5-4 retail calendars disagree — state which.

SaaS and ads

SaaS LTV:CAC is a ratio of two sketches. LTV often uses margin and a churn assumption; garbage in, confident slide out.

Churn rate / MRR tracks the leak and remaining recurring revenue. Logo churn ≠ revenue churn. Pair with LTV:CAC; do not replace one with the other.

CPM is cost per thousand impressions. It is an ads unit, not a subscription LTV, not a margin.

Crypto staking APY is a teaching yield sketch. Variable rewards, slashing, and token price are the real story. Not bank APR. Not NPV of a factory.

Personal compound interest still belongs on the savings hub linked above.

Developer-IT: addresses, encodings, fixtures

Subnet calculator : CIDR prefix, mask, host counts, network/broadcast in IPv4 teaching. IPv6 is a different animal if the page is v4-only — read the fields.

Hex / binary converter is representation. Color #FF00AA, bitmask 0x0F, ASCII hex dumps. Converting a mask to hex does not subnet for you.

Image resize calculator is pixel dimensions and maybe aspect. Not RAID capacity (bytes on disk) even though both mention “size.”

CSV test data generator builds fixture rows. Not a statistics RNG for inference, not production PII.

UUID generator mints identifiers. Uniqueness is probabilistic in v4. Not a password (passwords should be secrets; UUIDs are often public IDs).

Other utilities people still search

Dog age calculator is a pop-culture mapping, not veterinary science. Novelty with a disclaimer. Not a human age calculator (dates hub).

Password entropy calculator estimates bits under a model of how the password was chosen. A generator that samples uniformly is a different page: password generator. Do not type the live password into a blog post; use the generator, store in a manager.

bcrypt / Argon2 cost calculator is about work factor / time on a hashing scheme. Slow hashes are not extra entropy if the password is dog123. Ops teaching, not a subnet tool.

RAID storage capacity maps raw disks to usable bytes for RAID 0/1/5/6/10 teaching. Rebuild, checksum, and filesystem overhead still bite. Not an image-pixel count.

Acoustic room mode calculator estimates axial modes from room dimensions (c/2L teaching). Not a decibel distance outdoor model (physics hub), not a RAID.

Worked Monday morning

9:00 — “What’s our APR on this facility vs IRR on the expansion?” Two finance pages, two sentences on the slide.
10:00 — GMROI on the SKU, margin on the category, fiscal week of the promo.
11:00 — Churn this month, LTV:CAC on the deck, CPM on the campaign. Do not average them.
14:00 — New VLAN: subnet first, hex only if you are reading a dump.
15:00 — Fixtures: CSV generator; public IDs: UUID; user login secrets: generator + entropy discussion + hash cost in the auth service, not bingo.
16:00 — NAS: RAID capacity. Studio: room modes. Leave dog-age tabs closed during the incident.

Sign conventions, CIDR, and usable terabytes

NPV: cash flows −100, 40, 40, 40, 40 at 10%. You must use period alignment (end of year teaching). If the second sign flip appears, IRR hunting gets messy — prefer NPV at a stated hurdle. APR 12% with monthly compounding is not 1% per month in every legal definition; read the page’s compounding field.

Margin: sales 200, cost 150 → margin 25% on sales, markup 33% on cost. GMROI: gross margin 50,000 / inventory 20,000 = 2.5. Depreciation: 12,000 cost, 2,000 salvage, 5 years → 2,000 per year straight line. Fiscal week 2026-W14 in ISO is not necessarily “April week 2” in a 4-5-4 retail file.

SaaS: 5% monthly logo churn is not 60% yearly if you compound survivors (survival (0.95)^12 ≈ 54% remain, so ~46% annualized logo loss in that cartoon). LTV that assumes 5% churn and 80% margin will move a lot if churn is 8%. CPM 12 means $12 per 1000 impressions; 200,000 impressions cost $2,400 before fees. Staking 8% APY on a token that drops 50% is not an 8% real result — and still not advice.

IPv4 /24 has 256 addresses, 254 hosts in the classic teaching (network + broadcast reserved). /32 is a single host route. Hex FF is 255 decimal is 11111111 binary. Image 4000×3000 resized to 1000 px wide at locked aspect is 1000×750 — pixels, not GiB on RAID 5.

RAID 5 with four 4 TB disks is often taught as 12 TB usable; formats and spares eat more. Room 4 m × 5 m × 2.5 m axial modes: f = 343/(2L) gives 42.9 Hz along 4 m (using 343 m/s). Dog age “×7” is folklore; say so.

UUIDv4: 122 random bits of the 128. Entropy of Password1! is a few bits under a dictionary model, not 11 characters × 7 bits. Bcrypt cost 12 vs 13 roughly doubles work. CSV fixtures with real emails are a leak; use the generator.

One company, many tabs

Retail + SaaS + a small office: the loan on the van quotes an APR; the warehouse robot project wants NPV and IRR at a 12% hurdle; they are not a weighted average. Shelf: margin on coffee 40% on sales, GMROI 3.1 because inventory turns. Books: espresso machine straight-line over 5 years. The promo is fiscal week 32, which is not ISO week 32 in this company — the fiscal-week page exists so someone stops arguing in Slack.

Growth: CAC 80, LTV sketch 400, ratio 5; monthly churn 4% of logos. Ads: CPM 9.50. A staking APY dashboard on a treasury wallet is a separate sketch and a separate risk committee — still not the compound-interest vacation fund article, but closer to that article than to CPM.

IT: office VLAN /24, printer NIC shows mask FFFFFF00 in hex (hex converter), not a new subnet. Product shots resized to 1600 px wide (image resize). QA loads 10,000 fake users (CSV). Each user id is a UUID, not a password. Login passwords come from a generator; the security review talks entropy of the policy and bcrypt cost 12 on the auth box. File server: four disks RAID 10 usable capacity. Podcast studio: room modes from 3.2 × 4.1 × 2.6 m. Someone’s “dog years” Slack bot uses the novelty page and should not be in the incident channel.

If a tab does not map to one row of the table at the top of this article, you are either in the compound/savings hub, the percent-math hub, or a different silo entirely.

What this hub will not do

It will not price a cap table, file VAT, or harden a production password store. It will not pick RAID 6 vs cloud object storage for your RPO. It will not tell you to stake tokens. It will not treat dog-age as biology. It will not treat a UUID as a secret.

What it will do is keep APR next to loans, IRR/NPV next to projects, margin/GMROI next to shops, LTV/churn/CPM next to software ads, and CIDR next to masks. Search for “rate calculator” might mean APR, IRR, churn, staking APY, or even running pace (sports silo). Search for “size calculator” might mean image pixels, RAID bytes, or pet crates (household). Search for “generator” might mean UUID, CSV, password, bingo, or stats RNG. This page owns the work-ish subset; the rest have homes.

When a founder tab-spams NPV, LTV, and CPM into one “growth number,” make three numbered lines. When an intern hex-encodes a subnet and calls it security, send them to entropy and hash cost instead. When finance asks for “the rate,” ask whether they mean APR on a facility, IRR on a project, churn on a book of logos, or a staking dashboard — four rates, four URLs, four audiences. Neighbor hubs: markup/discount and percent-of live under percent-math; personal compound interest under the savings article; household password generator under dates-household; image pixels are not RAID; dog-age is not veterinary BMI. If the blank is a CIDR prefix, skip every finance URL even if the ticket also mentions “margin” as leftover switchports. If the blank is a currency NPV, skip every subnet URL even if the project is “the network refresh.” Two jobs, two tabs, two sentences on the ticket. That is the whole silo. Do not average them. Do not invent a fifth rate that is “the average of APR and CPM.”

Practical takeaway

Finance leftovers on this page are firm and shop dialects (APR, NPV, IRR, margin, GMROI, depreciation, fiscal week, SaaS, CPM, staking sketch). Household savings rates stay on the compound hub. Ops leftovers are representation and capacity (subnet, hex, images, CSV, UUID, RAID, hash cost, entropy, room modes). Novelty dog-age is outbound-only. If the job is a Punnett square or a rain barrel, you opened the wrong silo.