diff --git a/extension.js b/extension.js
index 8dd1cba..d8d6b31 100644
--- a/extension.js
+++ b/extension.js
@@ -1,5 +1,3 @@
-const Lang = imports.lang;
-const UPower = imports.gi.UPowerGlib;
 const BaseIndicator = imports.ui.status.power.Indicator;
 const ExtensionUtils = imports.misc.extensionUtils;
 const Panel = imports.ui.main.panel;
@@ -28,9 +26,7 @@ var TPIndicator = GObject.registerClass(
             super._init();
 
             this.settings = ExtensionUtils.getSettings('org.gnome.shell.extensions.tp_wattmeter');
-
-            // to detect changes FIXME: a better way?
-            this.last_period_val = this.settings.get_double('period-sec');
+            this.settings.connect('changed::period-sec', () => { this._spawn(); });  // restart timers on setting change
 
             this.readings = [];
             this.last_value = 0.0;
@@ -71,13 +67,6 @@ var TPIndicator = GObject.registerClass(
             const power = parseFloat(this._read_file(POWER_NOW), 0) / 1000000;
             this.readings.push(power)
 
-            const period_now = this.settings.get_double('period-sec');
-            if (period_now.toFixed(1) != this.last_period_val.toFixed(1)) {
-                // period changed, re-spawn
-                this._spawn();
-                this.last_period_val = period_now;
-            };
-
             const avg_of = this.settings.get_int('avg-of');
             if (this.readings.length >= avg_of) {
                 this.last_value = this.readings.reduce((acc, elem) => acc + elem, 0.0) / this.readings.length; // simple mean
@@ -94,12 +83,13 @@ var TPIndicator = GObject.registerClass(
             this.tm_measure = GLib.timeout_add(
                 GLib.PRIORITY_DEFAULT,
                 this.settings.get_double('period-sec') * 1000,
-                Lang.bind(this, this._measure)
+                this._measure.bind(this),
             );
         }
 
         _stop() {
             GLib.source_remove(this.tm_measure);
+            this.tm_measure = null;
         }
     }
 );
diff --git a/prefs.js b/prefs.js
index 9c51686..c545f72 100644
--- a/prefs.js
+++ b/prefs.js
@@ -1,6 +1,6 @@
 'use strict';
 
-const { Adw, Gio, Gtk } = imports.gi;
+const { Gio, Gtk } = imports.gi;
 
 const ExtensionUtils = imports.misc.extensionUtils;
 const Me = ExtensionUtils.getCurrentExtension();
@@ -10,21 +10,86 @@ function init() {
 }
 
 function fillPreferencesWindow(window) {
-    const settings = ExtensionUtils.getSettings('org.gnome.shell.extensions.tp_wattmeter');
+    // Gnome 42+: GTK5 & libadwaita
+    const Adw = imports.gi.Adw;
+
+    const settings = ExtensionUtils.getSettings(SETTINGS_ID);
 
     const page = new Adw.PreferencesPage();
     const group = new Adw.PreferencesGroup();
     page.add(group);
 
     // history depth
-    const avg_row = new Adw.ActionRow({ title: 'Show average of this many measurements' });
+    const avg_row = new Adw.ActionRow({ title: LBL_AVG });
     group.add(avg_row);
 
+    const avg_spin = makeAvgOfSpin(settings);
+    avg_row.add_suffix(avg_spin);
+    avg_row.activatable_widget = avg_spin;
+
+    // measure period
+    const period_row = new Adw.ActionRow({ title: LBL_PERIOD });
+    group.add(period_row);
+
+    const period_spin = makePeriodSpin(settings);
+    period_row.add_suffix(period_spin);
+    period_row.activatable_widget = period_spin;
+
+    // done
+    window.add(page);
+}
+
+
+function buildPrefsWidget() {
+    // Gnome 41-: GTK4 bare
+    const settings = ExtensionUtils.getSettings(SETTINGS_ID);
+
+    // history
+    const avg_lbl = new Gtk.Label({label: LBL_AVG});
+    const avg_spin = makeAvgOfSpin(settings);
+    
+    const avg_box = new Gtk.Box(); 
+    avg_box.set_spacing(10);
+    avg_box.set_orientation(Gtk.Orientation.HORIZONTAL);
+    avg_box.prepend(avg_lbl);
+    avg_box.append(avg_spin);
+
+    // period
+    const period_lbl = new Gtk.Label({label: LBL_PERIOD});
+    const period_spin = makePeriodSpin(settings);
+    
+    const period_box = new Gtk.Box(); 
+    period_box.set_spacing(10);
+    period_box.set_orientation(Gtk.Orientation.HORIZONTAL);
+    period_box.prepend(period_lbl);
+    period_box.append(period_spin);
+
+    // main
+    const main_box = new Gtk.Box(); 
+    main_box.set_spacing(25);
+    main_box.set_orientation(Gtk.Orientation.VERTICAL);
+    main_box.append(avg_box);
+    main_box.append(period_box);
+
+    // done
+    return main_box;
+}
+
+
+/** Common
+ */
+
+const SETTINGS_ID = 'org.gnome.shell.extensions.tp_wattmeter';
+const LBL_AVG = 'Show average of this many measurements';
+const LBL_PERIOD = 'Period between measurements in seconds';
+
+
+function makeAvgOfSpin(settings) {
     const avg_spin = new Gtk.SpinButton({
         climb_rate: 1,
         digits: 0,
         adjustment: new Gtk.Adjustment({
-            value: settings.get_uint('avg-of'),
+            value: settings.get_int('avg-of'),
             lower: 1,
             upper: 25,
             step_increment: 1,
@@ -36,13 +101,11 @@ function fillPreferencesWindow(window) {
         'value',
         Gio.SettingsBindFlags.DEFAULT
     );
-    avg_row.add_suffix(avg_spin);
-    avg_row.activatable_widget = avg_spin;
+    return avg_spin;
+}
 
-    // measure period
-    const period_row = new Adw.ActionRow({ title: 'Period between measurements in seconds' });
-    group.add(period_row);
 
+function makePeriodSpin(settings) {
     const period_spin = new Gtk.SpinButton({
         climb_rate: 1,
         digits: 1,
@@ -59,9 +122,5 @@ function fillPreferencesWindow(window) {
         'value',
         Gio.SettingsBindFlags.DEFAULT
     );
-    period_row.add_suffix(period_spin);
-    period_row.activatable_widget = period_spin;
-
-    // done
-    window.add(page);
+    return period_spin;
 }