fixup, add links, add changelog entry.

CHANGELOG.md

@@ -27,6 +27,8 @@ release.
   ([#2154](https://github.com/open-telemetry/opentelemetry-specification/pull/2154))
 - Mark In-memory, OTLP and Stdout exporter specs as Stable.
   ([#2175](https://github.com/open-telemetry/opentelemetry-specification/pull/2175))
+- Use UCUM units in Metrics Semantic Conventions.
+  ([#2199](https://github.com/open-telemetry/opentelemetry-specification/pull/2199))
 
 ### Logs
 

specification/metrics/semantic_conventions/faas-metrics.md

@@ -32,19 +32,19 @@ type and units.
 
 Below is a table of FaaS invocation metric instruments.
 
-| Name | Instrument | Unit | Unit (UCUM) | Description |
-|------|------------|------|-------------|-------------|
-| `faas.invoke_duration` | Histogram | milliseconds |`ms` | Measures the duration of the invocation |
+| Name | Instrument | Unit | Unit ([UCUM](README.md#instrument-units)) | Description |
+|------|------------|------|-------------------------------------------|-------------|
+| `faas.invoke_duration` | Histogram | milliseconds | `ms` | Measures the duration of the invocation |
 | `faas.init_duration` | Histogram | milliseconds | `ms` | Measures the duration of the function's initialization, such as a cold start |
 | `faas.coldstarts` | Counter | default unit | `{coldstarts}` | Number of invocation cold starts. |
 | `faas.errors` | Counter | default unit | `{errors}` | Number of invocation errors. |
-| `faas.executions` | Counter | default unit |`{executions}` | Number of successful invocations. |
+| `faas.executions` | Counter | default unit | `{executions}` | Number of successful invocations. |
 | `faas.timeouts` | Counter | default unit | `{timeouts}` | Number of invocation timeouts. |
 
 Optionally, when applicable:
 
-| Name | Instrument | Unit | Unit (UCUM) | Description |
-|------|------------|------|-------------|-------------|
+| Name | Instrument | Unit | Unit ([UCUM](README.md#instrument-units)) | Description |
+|------|------------|------|-------------------------------------------|-------------|
 | `faas.mem_usage` | Histogram | Bytes | `By` | Distribution of max memory usage per invocation |
 | `faas.cpu_usage` | Histogram | milliseconds | `ms` | Distribution of cpu usage per invocation |
 | `faas.net_io` | Histogram | Bytes | `By` | Distribution of net I/O usage per invocation |

specification/metrics/semantic_conventions/http-metrics.md

@@ -17,18 +17,18 @@ type and units.
 
 Below is a table of HTTP server metric instruments.
 
-| Name                          | Instrument                 | Unit         | Unit (UCUM)  | Description |
-|-------------------------------|----------------------------|--------------|--------------|-------------|
-| `http.server.duration`        | Histogram                  | milliseconds | `ms`         | measures the duration of the inbound HTTP request |
-| `http.server.active_requests` | Asynchronous UpDownCounter | requests     | `{requests}` | measures the number of concurrent HTTP requests that are currently in-flight |
+| Name                          | Instrument                 | Unit         | Unit ([UCUM](README.md#instrument-units)) | Description |
+|-------------------------------|----------------------------|--------------|-------------------------------------------|-------------|
+| `http.server.duration`        | Histogram                  | milliseconds | `ms`                                      | measures the duration of the inbound HTTP request |
+| `http.server.active_requests` | Asynchronous UpDownCounter | requests     | `{requests}`                              | measures the number of concurrent HTTP requests that are currently in-flight |
 
 ### HTTP Client
 
 Below is a table of HTTP client metric instruments.
 
-| Name                   | Instrument | Unit         | Unit (UCUM) | Description |
-|------------------------|------------|--------------|-------------|-------------|
-| `http.client.duration` | Histogram  | milliseconds | `ms`        | measure the duration of the outbound HTTP request |
+| Name                   | Instrument | Unit         | Unit ([UCUM](README.md#instrument-units)) | Description |
+|------------------------|------------|--------------|-------------------------------------------|-------------|
+| `http.client.duration` | Histogram  | milliseconds | `ms`                                      | measure the duration of the outbound HTTP request |
 
 ## Attributes
 

specification/metrics/semantic_conventions/rpc.md

@@ -31,8 +31,8 @@ MUST be of the specified type and units.
 
 Below is a table of RPC server metric instruments.
 
-| Name | Instrument | Unit | Unit (UCUM) | Description | Status | Streaming |
-|------|------------|------|-------------|-------------|--------|-----------|
+| Name | Instrument | Unit | Unit ([UCUM](README.md#instrument-units)) | Description | Status | Streaming |
+|------|------------|------|-------------------------------------------|-------------|--------|-----------|
 | `rpc.server.duration` | Histogram  | Bytes | `ms` | measures duration of inbound RPC | Recommended | N/A.  While streaming RPCs may record this metric as start-of-batch to end-of-batch, it's hard to interpret in practice. |
 | `rpc.server.request.size` | Histogram  | Bytes | `By` | measures size of RPC request messages (uncompressed) | Optional | Recorded per message in a streaming batch |
 | `rpc.server.response.size` | Histogram  | Bytes | `By` | measures size of RPC response messages (uncompressed) | Optional | Recorded per response in a streaming batch |
@@ -44,8 +44,8 @@ Below is a table of RPC server metric instruments.
 Below is a table of RPC client metric instruments.  These apply to traditional
 RPC usage, not streaming RPCs.
 
-| Name | Instrument | Unit | Unit (UCUM) | Description | Status | Streaming |
-|------|------------|------|-------------|-------------|--------|-----------|
+| Name | Instrument | Unit | Unit ([UCUM](README.md#instrument-units)) | Description | Status | Streaming |
+|------|------------|------|-------------------------------------------|-------------|--------|-----------|
 | `rpc.client.duration` | Histogram | milliseconds | `ms` | measures duration of outbound RPC | Recommended | N/A.  While streaming RPCs may record this metric as start-of-batch to end-of-batch, it's hard to interpret in practice. |
 | `rpc.client.request.size` | Histogram | Bytes | `By` | measures size of RPC request messages (uncompressed) | Optional | Recorded per message in a streaming batch |
 | `rpc.client.response.size` | Histogram | Bytes | `By` | measures size of RPC response messages (uncompressed) | Optional | Recorded per message in a streaming batch |