> For the complete documentation index, see [llms.txt](https://docs.force.xyz/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.force.xyz/perp-mechanics/external-price.md).

# External Price

The **external price** is a separate value, submitted alongside the oracle and mark prices, equal to the last price an external market actually set.

| Session      | External price                                                                       |
| ------------ | ------------------------------------------------------------------------------------ |
| **Cash**     | Equal to the oracle price                                                            |
| **Extended** | Equal to the oracle price                                                            |
| **Internal** | **Frozen** at the last externally priced value, while the oracle advances on its own |

Cash and Extended are both external sessions: a real market set the price, so the external price and the oracle price are the same number. They separate only in Internal, when no market is open and the oracle is advancing on the order book alone.

## What it is used for

**It bounds the mark price.** This is the important one. The mark price is restricted to within **±(1 / max leverage)** of the external price, so for a market with 20x maximum leverage the mark cannot sit more than 5% away from the last price a real market set.

| Market       | Max leverage | Mark bound around the external price |
| ------------ | ------------ | ------------------------------------ |
| FORCE-US10Y  | 20x          | ±5%                                  |
| FORCE-MORT30 | 10x          | ±10%                                 |

The bound matters most exactly where it is most needed. During Internal the external price is frozen, often for a whole weekend, so the bound is anchored to Friday's close and does not drift with the book. A trader who pushes a thin weekend book can move the oracle only within that band, no matter how far they push. It is the structural limit on low-liquidity manipulation, and it complements the [internal EMA](/perp-mechanics/oracle-price.md), which makes the oracle slow to move at all.

A consequence worth knowing: if a position's liquidation price falls outside the active bound, that position cannot be liquidated while the bound is in effect.

**It separates observed from derived.** The venue can always tell the difference between a price a market set and a price the oracle produced in the absence of one, without inspecting the session stamp.

{% hint style="info" %}
Force computes and submits the external price. The bound itself is enforced by Hyperliquid, not by the Force oracle. See Hyperliquid's HIP-3 documentation for how the exchange applies it.
{% endhint %}


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