diff --git a/firmware/inc/location.h b/firmware/inc/location.h
index 34741a7..7f66ea5 100644
--- a/firmware/inc/location.h
+++ b/firmware/inc/location.h
@@ -29,11 +29,10 @@
 #include "samd20.h"
 
 bool telemetry_location_tx_allow(void);
-void telemetry_location_update(int32_t lon_i, int32_t lat_i);
+void telemetry_location_update(int32_t lon_hn, int32_t lat_hn);
 
-bool latlon_in_aprs_zone(int32_t aprs_zone, int32_t aprs_zone_outline, float lon, float lat);
 bool aprs_location_tx_allow(void);
 int32_t aprs_location_frequency(void);
-void aprs_location_update(int32_t lon_i, int32_t lat_i);
+void aprs_location_update(int32_t lon_hn, int32_t lat_hn);
 
 #endif /* LOCATION_H */
diff --git a/firmware/src/location.c b/firmware/src/location.c
index 8b79149..b4e4104 100644
--- a/firmware/src/location.c
+++ b/firmware/src/location.c
@@ -73,11 +73,13 @@ bool point_in_polygon(const int32_t* poly, uint32_t points, int32_t x, int32_t y
 }
 /**
  * Returns if a latitude and longitude is in a polygon
+ *
+ * lat_hn, lon_hn in 100 nanodeg
  */
-bool latlon_in_polygon(const int32_t* poly, uint32_t points, float lon, float lat)
+bool latlon_in_polygon(const int32_t* poly, uint32_t points, int32_t lon_hn, int32_t lat_hn)
 {
-  int32_t x = (int32_t)round(lon * 1000 * 1000); // longitude: µdegrees
-  int32_t y = (int32_t)round(lat * 1000 * 1000); // latitude:  µdegrees
+  int32_t x = lon_hn / 10; /* longitude : 100 nano -> µdegrees */
+  int32_t y = lat_hn / 10; /* latitude  : 100 nano -> µdegrees */
 
   return point_in_polygon(poly, points, x, y);
 }
@@ -90,13 +92,15 @@ bool latlon_in_polygon(const int32_t* poly, uint32_t points, float lon, float la
 
 /**
  * Returns if a latitude and longitude is in a given no telem outline
+ *
+ * lat_hn, lon_hn in 100 nanodeg
  */
-bool latlon_in_no_telem_zone(int32_t no_telem_outline, float lon, float lat)
+bool latlon_in_no_telem_zone(int32_t no_telem_outline, int32_t lon_hn, int32_t lat_hn)
 {
   return latlon_in_polygon(
     no_telem_outlines[no_telem_outline],
     no_telem_outline_lengths[no_telem_outline],
-    lon, lat);
+    lon_hn, lat_hn);
 }
 /**
  * Return if telemetry should be transmitted in the current zone
@@ -109,19 +113,17 @@ bool telemetry_location_tx_allow(void)
 /**
  * Updates the current telemetry location based on the current lat/lon
  *
- * lat_i, lon_i in 100 nanodeg
+ * lat_hn, lon_hn in 100 nanodeg
  */
-void telemetry_location_update(int32_t lon_i, int32_t lat_i)
+void telemetry_location_update(int32_t lon_hn, int32_t lat_hn)
 {
   uint32_t outline;
-  float lat = lat_i / 10000000.0; /* degrees */
-  float lon = lon_i / 10000000.0; /* degrees */
 
   /* Were we in a telemetry outline last time? */
   if (current_no_telem_outline >= 0) {
 
     /* Are we still in this outline? */
-    if (latlon_in_no_telem_zone(current_no_telem_outline, lon, lat)) {
+    if (latlon_in_no_telem_zone(current_no_telem_outline, lon_hn, lat_hn)) {
       return; /* Still in this outline */
     }
   }
@@ -130,7 +132,7 @@ void telemetry_location_update(int32_t lon_i, int32_t lat_i)
   while (sizeof(no_telem_outlines)/sizeof(int32_t*) != 6);
   for (outline = 0; outline < sizeof(no_telem_outlines) / sizeof(int32_t*); outline++) {
 
-    if (latlon_in_no_telem_zone(outline, lon, lat)) { /* If we're in this zone */
+    if (latlon_in_no_telem_zone(outline, lon_hn, lat_hn)) { /* If we're in this zone */
 
       /* Record the current outline */
       current_no_telem_outline = outline;
@@ -146,13 +148,16 @@ void telemetry_location_update(int32_t lon_i, int32_t lat_i)
 
 /**
  * Returns if a latitude and longitude is in a given aprs zone outline
+ *
+ * lat_hn, lon_hn in 100 nanodeg
  */
-bool latlon_in_aprs_zone(int32_t aprs_zone, int32_t aprs_zone_outline, float lon, float lat)
+bool latlon_in_aprs_zone(int32_t aprs_zone, int32_t aprs_zone_outline,
+                         int32_t lon_hn, int32_t lat_hn)
 {
   return latlon_in_polygon(
     aprs_zones[aprs_zone].outlines[aprs_zone_outline],
     aprs_zones[aprs_zone].outline_lengths[aprs_zone_outline],
-    lon, lat);
+    lon_hn, lat_hn);
 }
 /**
  * Returns if aprs should be transmitted in the current zone
@@ -178,13 +183,11 @@ int32_t aprs_location_frequency(void)
 /**
  * Updates the aprs location based on the current lat/lon
  *
- * lat_i, lon_i in 100 nanodeg
+ * lat_hn, lon_hn in 100 nanodeg
  */
-void aprs_location_update(int32_t lat_i, int32_t lon_i)
+void aprs_location_update(int32_t lon_hn, int32_t lat_hn)
 {
   uint32_t z, outline;
-  float lat = lat_i / 10000000.0; /* degrees */
-  float lon = lon_i / 10000000.0; /* degrees */
 
   /* Were we in an aprs zone last time? */
   if (current_aprs_zone >= 0 && current_aprs_zone_outline >= 0) {
@@ -192,7 +195,7 @@ void aprs_location_update(int32_t lat_i, int32_t lon_i)
     /* Are we still in the outline? */
     if (latlon_in_aprs_zone(current_aprs_zone,
                             current_aprs_zone_outline,
-                            lon, lat)) {                    /* Still in outline */
+                            lon_hn, lat_hn)) {                    /* Still in outline */
       return;
     }
   }
@@ -202,7 +205,7 @@ void aprs_location_update(int32_t lat_i, int32_t lon_i)
 
     for (outline = 0; outline < aprs_zones[z].outline_count; outline++) {
 
-      if (latlon_in_aprs_zone(z, outline, lon, lat)) { /* If we're in this zone */
+      if (latlon_in_aprs_zone(z, outline, lon_hn, lat_hn)) { /* If we're in this zone */
 
         /* Record the current zone */
         current_aprs_zone = z;
diff --git a/firmware/test/tc/location_aprs.h b/firmware/test/tc/location_aprs.h
index 10a10e3..283d259 100644
--- a/firmware/test/tc/location_aprs.h
+++ b/firmware/test/tc/location_aprs.h
@@ -21,7 +21,11 @@ struct location_aprs_tc_results {
 /* Function */
 __verification__ void location_aprs_tc(void) {
 
-  aprs_location_update(location_aprs_tc_params.lon, location_aprs_tc_params.lat);
+  /* Supply co-ords in units of 100 nanodeg */
+  aprs_location_update(
+    (int32_t)(location_aprs_tc_params.lon * 10 * 1000 * 1000),
+    (int32_t)(location_aprs_tc_params.lat * 10 * 1000 * 1000)
+    );
 
   location_aprs_tc_results.tx_allow = aprs_location_tx_allow();
   location_aprs_tc_results.frequency = aprs_location_frequency();
diff --git a/firmware/test/tc/location_telemetry.h b/firmware/test/tc/location_telemetry.h
index f78bd1b..f37e148 100644
--- a/firmware/test/tc/location_telemetry.h
+++ b/firmware/test/tc/location_telemetry.h
@@ -20,7 +20,11 @@ struct location_telemetry_tc_results {
 /* Function */
 __verification__ void location_telemetry_tc(void) {
 
-  telemetry_location_update(location_telemetry_tc_params.lon, location_telemetry_tc_params.lat);
+  /* Supply co-ords in units of 100 nanodeg */
+  telemetry_location_update(
+    (int32_t)(location_telemetry_tc_params.lon * 10 * 1000 * 1000),
+    (int32_t)(location_telemetry_tc_params.lat * 10 * 1000 * 1000)
+    );
 
   location_telemetry_tc_results.tx_allow = telemetry_location_tx_allow();
 }
diff --git a/firmware/test/tc/location_telemetry.py b/firmware/test/tc/location_telemetry.py
index d2ff5ba..3ebad1a 100644
--- a/firmware/test/tc/location_telemetry.py
+++ b/firmware/test/tc/location_telemetry.py
@@ -62,6 +62,6 @@ class location_telemetry_tc:
         else:
             print_info("{} ({:.1f}, {:.1f}): Expected {}, Geofence {}".format(
                 name, params.lat, params.lon,
-                "Permitted" if expeced_tx_allow else "Not Permitted",
+                "Permitted" if expected_tx_allow else "Not Permitted",
                 "Permitted" if tx_allow else "Not Permitted"))
             return False