diff --git a/firmware/Pre-flight.md b/firmware/Pre-flight.md
index 3f88375..82edfe4 100644
--- a/firmware/Pre-flight.md
+++ b/firmware/Pre-flight.md
@@ -1,3 +1,12 @@
+## Updating Datapoints returned
+
+- UKHAS String
+  - Update `format_telemetry_string` in `src/main.c`
+  - Update `ukhas_format` in `tools/ukhas_format.py` so the aprs daemon can assemble valid backlog strings.
+- APRS telemetry
+  - `encode_telemetry` in `src/aprs.c`. This same format is re-used in backlog.
+  - `extract_telemetry` in `tools/extract_backlog.py` needs to be updated to parse this backlog.
+
 ## Pre-Flight Checklist ##
 
 - In `hw_config.h`
diff --git a/firmware/tools/ukhas_format.py b/firmware/tools/ukhas_format.py
index 5a481ff..fd8276a 100644
--- a/firmware/tools/ukhas_format.py
+++ b/firmware/tools/ukhas_format.py
@@ -28,11 +28,14 @@ def ukhas_format(datum, callsign):
     location_str = "{:.6f},{:.6f},{}".format(
         coords[0], coords[1], int(round(coords[2])))
 
-    # Everything
-    ukhas_str = "{},{},{},{},{},{},{},{},{}".format(
-        callsign, time_str, date_str, location_str,
-        datum['satellites'], datum['ttff'],
-        datum['battery'], datum['temperature_e'], datum['temperature_i']);
+    if callsign == 'UBSEDS14': # Telemetry string for flight UBESDS14
+        ukhas_str = "{},{},{},{},{},{},{},{},{}".format(
+            callsign, time_str, date_str, location_str,
+            datum['satellites'], datum['ttff'],
+            datum['battery'], datum['temperature_e'], datum['temperature_i']);
+
+    else: # Unknown callsign!
+         raise ValueException('ukhas_format.py does not know about callsign '+callsign)
 
     # Checksum
     crc16 = crcmod.mkCrcFun(0x11021, 0xFFFF, False, 0x0000)