implement a frequency input with switchable exponent

htdocs/lib/settings/FrequencyInput.js

@@ -0,0 +1,21 @@
+$.fn.frequencyInput = function() {
+    this.each(function(){
+        var $group = $(this);
+        var currentExponent = 0;
+        $input = $group.find('input');
+
+        var setExponent = function() {
+            var newExponent = parseInt($exponent.val());
+            var delta = currentExponent - newExponent;
+            $input.val(parseFloat($input.val()) * 10 ** delta);
+            currentExponent = newExponent;
+        };
+
+        $exponent = $group.find('select.frequency-exponent');
+        $exponent.on('change', setExponent);
+
+        // calculate initial exponent
+        $exponent.val(Math.floor(Math.log10($input.val()) / 3) * 3);
+        setExponent();
+    })
+};

htdocs/settings.js

@@ -7,4 +7,5 @@ $(function(){
     $('#rf_gain').gainInput();
     $('.optional-section').optionalSection();
     $('#scheduler').schedulerInput();
+    $('.frequency-input').frequencyInput();
 });