Add smart rounding for unit-converted display values

js/settings.js

@@ -23,6 +23,49 @@ function padZeros(val, length) {
     return str;
 }
 
+/**
+ * Round a converted value to fewer decimal places when doing so
+ * changes the value by less than 1%. For example, 328.08 ft (from 100m)
+ * becomes "328" and 9842.52 ft becomes "9843". Also rounds to the
+ * nearest 10/100/etc when within 1 of a boundary (e.g. 999 → "1000").
+ * Returns a string like toFixed().
+ */
+function smartRound(value, decimalPlaces) {
+    if (decimalPlaces < 2 || value === 0) {
+        return value.toFixed(decimalPlaces);
+    }
+    // Try removing decimal places (most aggressive first)
+    let best = null;
+    for (let dp = 0; dp <= decimalPlaces - 2; dp++) {
+        let rounded = parseFloat(value.toFixed(dp));
+        if (Math.abs(rounded - value) / Math.abs(value) < 0.01) {
+            best = rounded.toFixed(dp);
+            break;
+        }
+    }
+    // Try rounding to nearest 10, 100, etc. but only when the integer
+    // value is within 1 of a boundary (e.g. 999->1000, 1001->1000).
+    // Use absolute values for boundary detection to handle negatives.
+    if (best !== null) {
+        let intVal = Math.round(Math.abs(value));
+        for (let mag = 1; mag <= 3; mag++) {
+            let factor = Math.pow(10, mag);
+            let remainder = intVal % factor;
+            if (remainder <= 1 || remainder >= factor - 1) {
+                let rounded = Math.sign(value) * Math.round(Math.abs(value) / factor) * factor;
+                if (Math.abs(rounded - value) / Math.abs(value) < 0.01) {
+                    best = rounded.toFixed(0);
+                } else {
+                    break;
+                }
+            } else {
+                break;
+            }
+        }
+    }
+    return best !== null ? best : value.toFixed(decimalPlaces);
+}
+
 var Settings = (function () {
     let self = {};
 
@@ -534,7 +577,7 @@ var Settings = (function () {
             let mins = oldValue - (hours*60);
             newValue = ((hours < 0) ? padZeros(hours, 3) : padZeros(hours, 2)) + ':' + padZeros(mins, 2);
         } else {
-            newValue = Number((oldValue / multiplier)).toFixed(decimalPlaces);
+            newValue = smartRound(Number(oldValue / multiplier), decimalPlaces);
         }
 
         element.val(newValue);
@@ -688,3 +731,4 @@ var Settings = (function () {
 })();
 
 export default  Settings;
+export { smartRound };

tabs/osd.js

@@ -11,7 +11,7 @@ import { GUI, TABS } from './../js/gui';
 import MSP from './../js/msp';
 import MSPCodes from './../js/msp/MSPCodes';
 import mspHelper from './../js/msp/MSPHelper';
-import Settings from './../js/settings';
+import Settings, { smartRound } from './../js/settings';
 import { globalSettings } from './../js/globalSettings';
 import { PortHandler } from './../js/port_handler';
 import i18n from './../js/localization';
@@ -769,10 +769,10 @@ OSD.constants = {
                     case 0: // Imperial
                     case 3: // UK
                         // meters to miles
-                        return (value / 1609.344).toFixed(2);
+                        return smartRound(value / 1609.344, 2);
                     case 4: // GA
                         // metres to nautical miles
-                        return (value / 1852.001).toFixed(2);
+                        return smartRound(value / 1852.001, 2);
                     default: // Metric
                         return value;
                 }