diff --git a/libs/bluetooth/bluetooth.cpp b/libs/bluetooth/bluetooth.cpp
index e1f2db3e..75622de9 100644
--- a/libs/bluetooth/bluetooth.cpp
+++ b/libs/bluetooth/bluetooth.cpp
@@ -120,6 +120,7 @@ namespace bluetooth {
         registerWithDal(MICROBIT_ID_BLE, MICROBIT_BLE_EVT_DISCONNECTED, body);
     } 
 
+    const int8_t CALIBRATED_POWERS[] = {-49, -37, -33, -28, -25, -20, -15, -10};
     /**
     * Advertise an Eddystone URL
 	* @param url the url to transmit. Must be no longer than the supported eddystone url length, eg: "https://pxt.io/"
@@ -131,7 +132,7 @@ namespace bluetooth {
     //% help=bluetooth/advertise-url blockExternalInputs=1
     void advertiseUrl(StringData* url, int power, bool connectable) {
         power = min(MICROBIT_BLE_POWER_LEVELS-1, max(0, power));
-        int8_t level = MICROBIT_BLE_POWER_LEVEL[power];
+        int8_t level = CALIBRATED_POWERS[power];
         uBit.bleManager.advertiseEddystoneUrl(ManagedString(url), level, connectable);
         uBit.bleManager.setTransmitPower(power);
     }