> For the complete documentation index, see [llms.txt](https://docs.strikelabs.app/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.strikelabs.app/api-reference/notation.md).

# Notation

The vocabulary below is used consistently across every endpoint.

| Term             | Meaning                                                                                                                         |
| ---------------- | ------------------------------------------------------------------------------------------------------------------------------- |
| **symbol**       | The underlying, uppercase: `NVDA`, `TSLA`, `SMH`.                                                                               |
| **spot**         | The underlying's live price, from a 24/7 perpetual futures feed.                                                                |
| **series**       | One tradable option contract: an underlying, an expiry, a strike and a right.                                                   |
| **seriesId**     | The string name of a series. See [Series IDs](/api-reference/series-ids.md).                                                    |
| **sid**          | A small integer alias for a series, stable while the venue runs. Used by the binary maker wire; `seriesId` is the durable name. |
| **right**        | `C` for a call, `P` for a put.                                                                                                  |
| **expiryTs**     | Expiry as a unix timestamp in **seconds**.                                                                                      |
| **qty**          | Number of contracts. Fractional quantities are permitted.                                                                       |
| **premium**      | Price per contract, in dollars.                                                                                                 |
| **notional**     | `premium × qty` — what actually changes hands.                                                                                  |
| **mid**          | `(bid + ask) / 2`, present only when both sides are quoted.                                                                     |
| **iv**           | Implied volatility as a decimal: `0.366307` is 36.6%.                                                                           |
| **delta**        | Option delta, signed. Calls positive, puts negative.                                                                            |
| **openInterest** | Contracts outstanding in that series.                                                                                           |
| **volume**       | Contracts traded in that series today.                                                                                          |

## Money is integer micros

Internally every price and quantity is an integer of millionths — `1.25` is `1_250_000`. Nothing that touches money is a float, so no rounding drift can accumulate across fills, margin or settlement.

The JSON boundary converts to decimal numbers for convenience. When you need exactness, multiply by `1_000_000` and reason in integers on your side too.

## Timestamps

* `expiryTs` is in **seconds**.
* `ts` on a trade print, and `expiryCutoffMs`, are in **milliseconds**.

The mismatch is deliberate: expiries are a listing property and read better as seconds, while prints need millisecond ordering.

## Sessions

`sessionOpen` on a chain response reports whether the **underlying's** primary market is currently open. It does not gate trading. Strike's book is open at all times; the flag exists because quoting behaviour and hedging costs differ when the reference market is shut.


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