And now with inertia

src/cljs/swinging_needle_meter/core.cljs

@@ -1,6 +1,6 @@
 (ns swinging-needle-meter.core
   (:require [reagent.core :as reagent]
-            [re-frame.core :as re-frame]
+            [re-frame.core :as rf]
             [swinging-needle-meter.events]
             [swinging-needle-meter.subs]
             [swinging-needle-meter.views :as views]
@@ -14,12 +14,20 @@
     (enable-console-print!)
     (println "dev mode")))
 
+(defn dispatch-timer-event
+  []
+  (let [now (js/Date.)]
+    (rf/dispatch [:timer now])))  ;; <-- dispatch used
+
+;; call the dispatching function every tenth of a second
+(defonce do-timer (js/setInterval dispatch-timer-event 100))
+
 (defn mount-root []
-  (re-frame/clear-subscription-cache!)
+  (rf/clear-subscription-cache!)
   (reagent/render [views/main-panel]
                   (.getElementById js/document "app")))
 
 (defn ^:export init []
-  (re-frame/dispatch-sync [:initialize-db])
+  (rf/dispatch-sync [:initialize-db])
   (dev-setup)
   (mount-root))

src/cljs/swinging_needle_meter/events.cljs

@@ -8,17 +8,22 @@
  (fn  [_ _]
    state/default-state))
 
-;; The clock ticked.
+;; The clock ticked. Implement a mechanical swing.
 (re-frame/reg-event-db
  :timer
- (fn [db _]
-   db))
+ (fn [db [x value]]
+   (let [old-value (:old-value db)
+         target (:value db)
+         new-value (+ old-value (/ (- target old-value) 10))]
+   (assoc db :old-value new-value))))
 
 (re-frame/reg-event-db
  :set-value
  (fn [db [x value]]
-   (js/console.log (str :set-value " " x " " value))
-   (assoc db :value value)))
+   (assoc
+     (assoc db :old-value (:value db))
+     :value
+     value)))
 
 (re-frame/reg-event-db
  :set-setpoint

src/cljs/swinging_needle_meter/state.cljs

@@ -5,6 +5,7 @@
 (def default-state
   {:timer (js/Date.)
    :value 60
+   :old-value 0
    :setpoint 75
    :gradations 5
    :size 70

src/cljs/swinging_needle_meter/subs.cljs

@@ -12,6 +12,11 @@
  (fn [db]
    (:value db)))
 
+(re-frame/reg-sub
+ :old-value
+ (fn [db]
+   (:old-value db)))
+
 (re-frame/reg-sub
  :setpoint
  (fn [db]

src/cljs/swinging_needle_meter/views.cljs

@@ -11,14 +11,6 @@
 ;;  Demo: swinging-needle-meter
 ;; ------------------------------------------------------------------------------------
 
-(defn dispatch-timer-event
-  []
-  (let [now (js/Date.)]
-    (rf/dispatch [:timer now])))  ;; <-- dispatch used
-
-;; call the dispatching function every tenth of a second
-(defonce do-timer (js/setInterval dispatch-timer-event 100))
-
 
 (defn swinging-needle-demo
   []
@@ -69,7 +61,7 @@
                                           [v-box
                                            :gap      "20px"
                                            :children [[swinging-needle-meter
-                                                       :model     @(rf/subscribe [:value])
+                                                       :model     @(rf/subscribe [:old-value])
                                                        :setpoint  @(rf/subscribe [:setpoint])
                                                        :unit      @(rf/subscribe [:unit])
                                                        :min-value @(rf/subscribe [:min-val])