diff --git a/technical-reports/format/types.md b/technical-reports/format/types.md
index aa60e46..b7c3d74 100644
--- a/technical-reports/format/types.md
+++ b/technical-reports/format/types.md
@@ -51,12 +51,12 @@ $translucent-shadow: hsla(300, 100%, 50%, 0.5);
 
 ## Dimension
 
-Represents an amount of distance in a single dimension in the UI, such as a position, width, height, radius, or thickness. The `$type` property MUST be set to the string `dimension`. The value MUST be an object with `value` and `unit` keys.
+Represents an amount of distance in a single dimension in the UI, such as a position, width, height, radius, or thickness. The `$type` property MUST be set to the string `dimension`. The value MUST be an object with both `value` and `unit` keys.
 
 | Key     |   Type   | Required | Description                                                        |
 | :------ | :------: | :------: | :----------------------------------------------------------------- |
 | `value` | `number` |    Y     | An integer or floating-point value representing the numeric value. |
-| `unit`  | `string` |    Y     | A string specifying the units of measurement                       |
+| `unit`  | `string` |    Y     | Specify `"px"` or `"rem"`.                                         |
 
 For example:
 
@@ -85,8 +85,9 @@ For example:
 
 ### Validation
 
-- `$value.unit` may be any string. It is up to tooling to translate units into the appropriate platform.
-- `$value.unit` may NOT be an empty string (`""`).
+- `$value.unit` may only be `"px"` or `"rem"`.
+  - **px**: Represents an idealized pixel on the viewport. The equivalent in Android is `dp` and iOS is `pt`. Translation tools SHOULD therefore convert to these or other equivalent units as needed.
+  - **rem**: Represents a multiple of the system's default font size (which MAY be configurable by the user). 1rem is 100% of the default font size. The equivalent of 1rem on Android is 16sp. Not all platforms have an equivalent to rem, so translation tools MAY need to do a lossy conversion to a fixed px size by assuming a default font size (usually 16px) for such platforms.
 - `$value.unit` is still requird even if `$value.value` is `0`.
 
 ## Font family