diff --git a/README.md b/README.md
index 77e61f9..a27dada 100644
--- a/README.md
+++ b/README.md
@@ -47,6 +47,10 @@ a [PostgreSQL](https://www.postgresql.org/) database with a timeseries extension
 
 ## Deployment
 
+The `$CUSTOM_DOCKER_IP` environment variable can be used to set a custom
+IP address to bind ports. Default is `0.0.0.0`; `127.0.0.1` is a
+safe configuration (see https://github.com/docker/compose/issues/2999).
+
 ### Development
 
 ```bash
@@ -149,7 +153,7 @@ The sketch reads temperature and light from sensors.
 /* ... */
 
 void loop(void) {
-  const int postDelay = 10 * 1000;
+  const int postDelay = TELEMETRY_DELAY * 1000;
 
   unsigned int tempReading = analogRead(A0);
   unsigned int photocellReading = analogRead(A1);
diff --git a/arduino/README.md b/arduino/README.md
index a93dac3..dcd7f1b 100644
--- a/arduino/README.md
+++ b/arduino/README.md
@@ -52,7 +52,9 @@ The `EEPROM` can be completely erased setting the `ERASE_FIRST` macro to `1`.
 The following macros are available in the firmware (to be set at compile time):
 
 ```c
-#define DEBUG_TO_SERIAL 1  // debug on serial port
-#define USE_MQTT 1         // use mqtt protocol instead of http post
-#define USE_INTERNAL_NTP 0 // use default ntp server or the internal one
+#define DEBUG_TO_SERIAL   0   // debug on serial port
+#define USE_MQTT          1   // use mqtt protocol instead of http post
+#define USE_INTERNAL_NTP  1   // use default ntp server or the internal one
+#define TELEMETRY_DELAY  10   // second between telemetry samples
+#define AREF_VOLTAGE      3.3 // set aref voltage to 3.3v instead of default 5v
 ```
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