# `layer_mean()`
**Category:** Vertical summary
**Status:** stable

## Purpose
Compute a vertical layer summary.

## When to use
Use it when its declared input and output match the workflow. Prefer a narrower selection before any operation that may materialise values.

## When not to use
Do not use it to calculate `spatind` indicators or to bypass coordinate, CRS, unit, and provenance checks.

## Real signature
```r
layer_mean(x, depth)
```

## Arguments
- `x`: see the installed Rd manual for validation and defaults.
- `depth`: see the installed Rd manual for validation and defaults.

## Input and output
Input: **ocean_cube**. Output: **ocean_cube**.

## Backend support
Memory: **TRUE**. NetCDF: **TRUE**. Backend operations retain read-only semantics; materialisation is explicit.

## Dimensional effect
May change shape or return a non-cube analytical object; inspect dimensions/rows.

## Metadata
Units, coordinates, provenance, masks, and QA metadata are retained or reported where meaningful.

## Minimal executable check
```r
library(oceancube)
stopifnot(is.function(oceancube::layer_mean))
names(formals(oceancube::layer_mean))
```

## Example in a workflow
Typical position: `ocean_cube` → `layer_mean()` → `annual_index`. See the workflow scripts for a checked end-to-end example.

## Frequent errors and limitations
Invalid dimensions, selectors, units, CRS, source-file identity, optional dependencies, or unsupported grids are rejected explicitly. Read the function Rd page for exact diagnostics.

## Related functions
Previous: `ocean_cube`. Next: `annual_index`.