diff --git a/apps/altimeter/ChangeLog b/apps/altimeter/ChangeLog
index 8d21cf797..905152382 100644
--- a/apps/altimeter/ChangeLog
+++ b/apps/altimeter/ChangeLog
@@ -1,3 +1,4 @@
 0.01: New App!
 0.02: Actually upload correct code
 0.03: Display sea-level pressure, too, and allow calibration
+0.04: Switch to using system code for pressure calibration
diff --git a/apps/altimeter/app.js b/apps/altimeter/app.js
index de664af39..6e44161da 100644
--- a/apps/altimeter/app.js
+++ b/apps/altimeter/app.js
@@ -3,59 +3,54 @@ Bangle.setBarometerPower(true, "altimeter");
 g.clear(1);
 Bangle.loadWidgets();
 Bangle.drawWidgets();
-var zero = 0;
 var R = Bangle.appRect;
 var y = R.y + R.h/2;
 var MEDIANLENGTH = 20;
-var avr = [], median;
-var value = 0;
+var avr = [];
 
-function getStandardPressure(altitude) {
-  const P0 = 1013.25; // standard pressure at sea level in hPa
-  const T0 = 288.15; // standard temperature at sea level in K
-  const g0 = 9.80665; // standard gravitational acceleration in m/s^2
-  const R = 8.31432; // gas constant in J/(mol*K)
-  const M = 0.0289644; // molar mass of air in kg/mol
-  const L = -0.0065; // temperature lapse rate in K/m
-
-  const temperature = T0 + L * altitude; // temperature at the given altitude
-  const pressure = P0 * Math.pow((temperature / T0), (-g0 * M) / (R * L)); // pressure at the given altitude
-
-  return pressure;
-}
-
-function convertToSeaLevelPressure(pressure, altitude) {
-  return 1013.25 * (pressure / getStandardPressure(altitude));
+function fmt(t) {
+  if ((t > -100) && (t < 1000))
+    t = t.toFixed(1);
+  else
+    t = t.toFixed(0);
+  return t;
 }
 
 Bangle.on('pressure', function(e) {
   while (avr.length>MEDIANLENGTH) avr.pop();
   avr.unshift(e.altitude);
-  median = avr.slice().sort();
+  let median = avr.slice().sort();
   g.reset().clearRect(0,y-30,g.getWidth()-10,R.h);
   if (median.length>10) {
     var mid = median.length>>1;
-    value = E.sum(median.slice(mid-4,mid+5)) / 9;
-    t = value-zero;
-    if ((t > -100) && (t < 1000))
-      t = t.toFixed(1);
-    else
-      t = t.toFixed(0);
-    g.setFont("Vector",50).setFontAlign(0,0).drawString(t, g.getWidth()/2, y);
-    sea = convertToSeaLevelPressure(e.pressure, value-zero);
-    t = sea.toFixed(1) + " " + e.temperature.toFixed(1);
-    if (0) {
+    var value = E.sum(median.slice(mid-4,mid+5)) / 9;
+  } else {
+    var value = median[median.length>>1];
+  }
+  t = fmt(value);
+
+  g.setFont("Vector",50).setFontAlign(0,0).drawString(t, g.getWidth()/2, y);
+
+  let o = Bangle.getOptions();
+  let sea = o.seaLevelPressure;
+  t = sea.toFixed(1) + " " + e.temperature.toFixed(1);
+  if (0) {
       print("alt raw:", value.toFixed(1));
       print("temperature:", e.temperature);
       print("pressure:", e.pressure);
       print("sea pressure:", sea);
-      print("std pressure:", getStandardPressure(value-zero));
-    }
-    g.setFont("Vector",25).setFontAlign(-1,0).drawString(t,
-                                                        10, R.y+R.h - 35);
   }
+    g.setFont("Vector",25).setFontAlign(-1,0).drawString(t, 10, R.y+R.h - 35);
 });
 
+function setPressure(m, a) {
+  o = Bangle.getOptions();
+  print(o);
+  o.seaLevelPressure = o.seaLevelPressure * m + a;
+  Bangle.setOptions(o);
+  avr = [];
+}
+
 print(g.getFonts());
 g.reset();
 g.setFont("Vector:15");
@@ -63,9 +58,9 @@ g.setFontAlign(0,0);
 g.drawString(/*LANG*/"ALTITUDE (m)", g.getWidth()/2, y-40);
 g.drawString(/*LANG*/"SEA L (hPa) TEMP (C)", g.getWidth()/2, y+62);
 g.flip();
-g.setFont("6x8").setFontAlign(0,0,3).drawString(/*LANG*/"ZERO", g.getWidth()-5, g.getHeight()/2);
+g.setFont("6x8").setFontAlign(0,0,3).drawString(/*LANG*/"STD", g.getWidth()-5, g.getHeight()/2);
 Bangle.setUI("updown", btn=> {
-  if (!btn) zero=value;
-  if (btn<0) zero-=5;
-  if (btn>0) zero+=5;
+  if (!btn) setPressure(0, 1013.25);
+  if (btn<0) setPressure(1, 1);
+  if (btn>0) setPressure(1, -1);
 });
diff --git a/apps/altimeter/metadata.json b/apps/altimeter/metadata.json
index 8bf3772ed..ff5eb9935 100644
--- a/apps/altimeter/metadata.json
+++ b/apps/altimeter/metadata.json
@@ -1,6 +1,6 @@
 { "id": "altimeter",
   "name": "Altimeter",
-  "version":"0.03",
+  "version":"0.04",
   "description": "Simple altimeter that can display height changed using Bangle.js 2's built in pressure sensor.",
   "icon": "app.png",
   "tags": "tool,outdoors",