tomcarman · maniflopi · Jan 2, 2026
diff --git a/web/src/components/MotionFastestAircraft.svelte b/web/src/components/MotionFastestAircraft.svelte
@@ -1,15 +1,16 @@
 <script>
     import MotionStats from './MotionStats.svelte';
     import { IconRocket } from '@tabler/icons-svelte';
+    import { speedUnit, formatSpeed } from '../stores/preferences';
 
-    const columns = [
+    $: columns = [
         { header: 'Reg', field: 'registration', class: 'font-mono whitespace-nowrap' },
         { header: 'Type', field: 'type' },
         // { header: 'Flight', field: 'flight' },
         { 
-            header: 'Speed', 
+            header: `Speed`, 
             field: 'ground_speed',
-            formatter: (value) => value ? `${value.toLocaleString()} kts` : '-'
+            formatter: (value) => formatSpeed(value, $speedUnit)
         },
         { 
             header: 'First Seen', 

diff --git a/web/src/components/MotionHighestAircraft.svelte b/web/src/components/MotionHighestAircraft.svelte
@@ -1,15 +1,16 @@
 <script>
     import MotionStats from './MotionStats.svelte';
     import { IconArrowUpDashed } from '@tabler/icons-svelte';
+    import { altitudeUnit, formatAltitude } from '../stores/preferences';
 
-    const columns = [
+    $: columns = [
         { header: 'Reg', field: 'registration', class: 'font-mono' },
         { header: 'Model', field: 'type' },
         // { header: 'Flight', field: 'flight' },
         { 
-            header: 'Altitude', 
+            header: `Altitude`, 
             field: 'barometric_altitude',
-            formatter: (value) => value ? `${value.toLocaleString()} ft` : '-'
+            formatter: (value) => formatAltitude(value, $altitudeUnit)
         },
         { 
             header: 'First Seen', 

diff --git a/web/src/components/MotionLowestAircraft.svelte b/web/src/components/MotionLowestAircraft.svelte
@@ -1,15 +1,16 @@
 <script>
     import MotionStats from './MotionStats.svelte';
     import { IconArrowDownDashed } from '@tabler/icons-svelte';
+    import { altitudeUnit, formatAltitude } from '../stores/preferences';
 
-    const columns = [
+    $: columns = [
         { header: 'Reg', field: 'registration', class: 'font-mono' },
         { header: 'Model', field: 'type' },
         // { header: 'Flight', field: 'flight' },
         { 
-            header: 'Altitude', 
+            header: `Altitude`, 
             field: 'barometric_altitude',
-            formatter: (value) => value ? `${value.toLocaleString()} ft` : '-'
+            formatter: (value) => formatAltitude(value, $altitudeUnit)
         },
         { 
             header: 'First Seen', 

diff --git a/web/src/components/MotionSlowestAircraft.svelte b/web/src/components/MotionSlowestAircraft.svelte
@@ -1,15 +1,16 @@
 <script>
     import MotionStats from './MotionStats.svelte';
     import { IconWalk } from '@tabler/icons-svelte';
+    import { speedUnit, formatSpeed } from '../stores/preferences';
 
-    const columns = [
+    $: columns = [
         { header: 'Reg', field: 'registration', class: 'font-mono' },
         { header: 'Type', field: 'type' },
         // { header: 'Flight', field: 'flight' },
         { 
-            header: 'Speed', 
+            header: `Speed`, 
             field: 'ground_speed',
-            formatter: (value) => value ? `${value.toLocaleString()} kts` : '-'
+            formatter: (value) => formatSpeed(value, $speedUnit)
         },
         { 
             header: 'First Seen', 

diff --git a/web/src/components/Settings.svelte b/web/src/components/Settings.svelte
@@ -1,6 +1,7 @@
 <script>
     import { onMount } from 'svelte';
     import { settings } from '../stores/settings';
+    import { speedUnit, altitudeUnit, SPEED_UNITS, ALTITUDE_UNITS } from '../stores/preferences';
     import { IconBrandGithub } from '@tabler/icons-svelte';
 
 
@@ -16,6 +17,7 @@
 
     const menuItems = [
         { id: 'display', label: 'Display' },
+        { id: 'preferences', label: 'Preferences' },
         { id: 'about', label: 'About' }
     ];
 
@@ -191,6 +193,50 @@
                             </div>
                         </form>
 
+                    {:else if activeMenuItem === 'preferences'}
+                        <h4 class="text-lg font-semibold mb-6">Preferences</h4>
+                        <div class="space-y-8">
+
+                            <!-- Speed Units -->
+                            <div>
+                                <p class="text-xl font-extralight tracking-wider mb-4">Speed Units</p>
+                                <div class="form-control flex flex-row gap-10">
+                                    {#each Object.values(SPEED_UNITS) as unit}
+                                        <label class="label cursor-pointer justify-start gap-4">
+                                            <input 
+                                                type="radio" 
+                                                name="speed-unit" 
+                                                class="radio radio-primary" 
+                                                value={unit.value}
+                                                bind:group={$speedUnit} 
+                                            />
+                                            <span class="label-text">{unit.label} ({unit.value})</span> 
+                                        </label>
+                                    {/each}
+                                </div>
+                            </div>
+
+                            <!-- Altitude Units -->
+                            <div>
+                                <p class="text-xl font-extralight tracking-wider mb-4">Altitude Units</p>
+                                <div class="form-control flex flex-row gap-10">
+                                    {#each Object.values(ALTITUDE_UNITS) as unit}
+                                        <label class="label cursor-pointer justify-start gap-4">
+                                            <input 
+                                                type="radio" 
+                                                name="altitude-unit" 
+                                                class="radio radio-primary" 
+                                                value={unit.value}
+                                                bind:group={$altitudeUnit}
+                                            />
+                                            <span class="label-text">{unit.label} ({unit.value})</span> 
+                                        </label>
+                                    {/each}
+                                </div>
+                            </div>
+
+                        </div>
+
                     {:else if activeMenuItem === 'about'}
                         <div class="text-center mx-auto">
                             <div class="flex items-center justify-center gap-6 mb-2">
@@ -217,7 +263,9 @@
                     {/if}
                 </div>
 
-                {#if activeMenuItem !== 'about'}
+
+
+                {#if activeMenuItem === 'display'}
                     <div class="modal-action justify-end">
                         <button
                             class="btn btn-primary"

diff --git a/web/src/stores/preferences.js b/web/src/stores/preferences.js
@@ -0,0 +1,117 @@
+import { writable } from 'svelte/store';
+
+/**
+ * Indicates if the code is running in a browser environment.
+ * Used to avoid errors when accessing localStorage on the server (SSR).
+ * @type {boolean}
+ */
+const browser = typeof window !== 'undefined';
+
+/**
+ * Creates a Svelte store that persists its value to localStorage.
+ * 
+ * If running in the browser, it attempts to read the saved value.
+ * It also subscribes to store changes to automatically update localStorage.
+ * 
+ * @param {string} key - The unique key to save the value in localStorage.
+ * @param {*} initialValue - The default initial value if nothing is saved.
+ * @returns {import('svelte/store').Writable<*>} A writable Svelte store.
+ */
+const createPersistedStore = (key, initialValue) => {
+    // Check if we're in the browser and have a saved value
+    const savedValue = browser ? localStorage.getItem(key) : null;
+    const store = writable(savedValue || initialValue);
+
+    if (browser) {
+        store.subscribe((value) => {
+            localStorage.setItem(key, value);
+        });
+    }
+
+    return store;
+};
+
+/**
+ * Definition of available speed units.
+ * Each unit contains its display label, internal value, and conversion factor from Knots.
+ * 
+ * @constant
+ * @type {Object.<string, {label: string, value: string, factor: number}>}
+ */
+export const SPEED_UNITS = {
+    /** Knots (Base unit for aviation) */
+    KTS: { label: 'Knots', value: 'kts', factor: 1 },
+    /** Miles per hour */
+    MPH: { label: 'MPH', value: 'mph', factor: 1.15078 },
+    /** Kilometers per hour */
+    KMH: { label: 'km/h', value: 'km/h', factor: 1.852 },
+};
+
+/**
+ * Definition of available altitude units.
+ * Each unit contains its label, value, and conversion factor from Feet.
+ * 
+ * @constant
+ * @type {Object.<string, {label: string, value: string, factor: number}>}
+ */
+export const ALTITUDE_UNITS = {
+    /** Feet (Base unit for aviation) */
+    FT: { label: 'Feet', value: 'ft', factor: 1 },
+    /** Meters */
+    M: { label: 'Meters', value: 'm', factor: 0.3048 },
+};
+
+// The stores
+
+/**
+ * Store for the user selected speed unit.
+ * Persists in localStorage under the key 'settings_speed_unit'.
+ * @type {import('svelte/store').Writable<string>}
+ */
+export const speedUnit = createPersistedStore('settings_speed_unit', 'kts');
+
+/**
+ * Store for the user selected altitude unit.
+ * Persists in localStorage under the key 'settings_altitude_unit'.
+ * @type {import('svelte/store').Writable<string>}
+ */
+export const altitudeUnit = createPersistedStore('settings_altitude_unit', 'ft');
+
+
+// Helpers for formatting
+
+/**
+ * Formats a speed value (in knots) to the specified unit.
+ * 
+ * @param {number|null} knots - The speed in knots (raw API value).
+ * @param {string} unitValue - The code of the desired unit (e.g. 'kts', 'mph', 'km/h').
+ * @returns {string} The formatted speed with its unit (e.g. "150 km/h") or "-" if value is null.
+ */
+export const formatSpeed = (knots, unitValue) => {
+    if (knots === null || knots === undefined) return '-';
+
+    // Find unit object, or default to Knots if not found
+    const unit = Object.values(SPEED_UNITS).find(u => u.value === unitValue) || SPEED_UNITS.KTS;
+    const val = knots * unit.factor;
+
+    // Format without decimals
+    return `${val.toLocaleString(undefined, { maximumFractionDigits: 0 })} ${unit.value}`;
+};
+
+/**
+ * Formats an altitude value (in feet) to the specified unit.
+ * 
+ * @param {number|null} feet - The altitude in feet (raw API value).
+ * @param {string} unitValue - The code of the desired unit (e.g. 'ft', 'm').
+ * @returns {string} The formatted altitude with its unit (e.g. "1000 m") or "-" if value is null.
+ */
+export const formatAltitude = (feet, unitValue) => {
+    if (feet === null || feet === undefined) return '-';
+
+    // Find unit object, or default to Feet if not found
+    const unit = Object.values(ALTITUDE_UNITS).find(u => u.value === unitValue) || ALTITUDE_UNITS.FT;
+    const val = feet * unit.factor;
+
+    // Format without decimals
+    return `${val.toLocaleString(undefined, { maximumFractionDigits: 0 })} ${unit.value}`;
+};