First pass, buttons not rendering

src/blocks/activity/edit.js

@@ -1,6 +1,7 @@
 /* global wp, wpStrava */
 import EmbedPlaceholder from './embed-placeholder';
 import EmbedControls from './embed-controls';
+import SOMOverride from './som-override';
 
 const { __ } = wp.i18n;
 const { Component } = wp.element;
@@ -98,6 +99,9 @@ class Edit extends Component {
 							checked={ displayMarkers }
 							onChange={ (checked ) => this.toggleDisplayMarkers( checked ) }
 						/>
+						<SOMOverride
+							onChange={ ( value ) => this.props.setAttributes( { som: value } ) }
+						/>
 					</PanelBody>
 				</InspectorControls>
 			</>

src/blocks/activity/index.js

@@ -18,7 +18,11 @@ registerBlockType( 'wp-strava/activity', {
 		displayMarkers: {
 			type: 'boolean',
 			default: false,
-		}
+		},
+		som: {
+			type: 'string',
+			default: null,
+		},
 	},
 	edit,
 	save: () => null,

src/blocks/activity/som-override.js

@@ -0,0 +1,56 @@
+/**
+ * External dependencies
+ */
+import mapValues from 'lodash';
+
+/**
+ * WordPress dependencies
+ */
+import {
+	Button,
+	ButtonGroup,
+} from '@wordpress/components';
+import { __ } from '@wordpress/i18n';
+
+const SOM_PRESETS = {
+	'english': __( 'English', 'wp-strava' ),
+	'metric':  __( 'Metric', 'wp-strava' ),
+};
+
+export default function SOMOverride( {
+	onChange,
+} ) {
+
+	function updateSOM( newSOM ) {
+		return () => {
+			onChange( { som: newSOM } );
+		};
+	}
+
+	return (
+		<>
+			<div className="block-editor-som-control">
+				<ButtonGroup aria-label={ __( 'System of Measure (override from Settings)' ) }>
+					{ mapValues( SOM_PRESETS, ( key, label ) => {
+						return (
+							<Button
+								key={ key }
+								isSmall
+								isPrimary={ true }
+								isPressed={ true }
+								onClick={ updateSOM(
+									key
+								) }
+							>
+								{ label }
+							</Button>
+						);
+					} ) }
+				</ButtonGroup>
+				<Button isSmall onClick={ updateSOM() }>
+					{ __( 'Reset' ) }
+				</Button>
+			</div>
+		</>
+	);
+}