diff --git a/Cargo.toml b/Cargo.toml
index 89f4a11..1f58d57 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -2,6 +2,7 @@
 name = "rust-sensor"
 version = "0.1.0"
 authors = ["Klemens Schölhorn <klemens@schoelhorn.eu>"]
+edition = "2018"
 
 [dependencies]
 i2csensors = "0.1"
diff --git a/src/main.rs b/src/main.rs
index 84f5486..ee13265 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,38 +3,94 @@ extern crate i2cdev_bmp280;
 extern crate i2csensors;
 extern crate si7021;
 
-use i2cdev::linux::LinuxI2CDevice;
+use i2cdev::linux::{LinuxI2CDevice, LinuxI2CError};
 use i2cdev_bmp280::*;
-use si7021::*;
 use i2csensors::{Barometer, Hygrometer, Thermometer};
-
+use si7021::{Si7021, SI7021_I2C_ADDRESS};
 use std::env;
 
-fn main() {
-    let i2c_path = env::args().skip(1).next().expect("i2c bus path (eg. /dev/i2c-1)");
+static BMP280_I2C_ADDRESS: u16 = 0x76;
 
-    i2c_sensors(&i2c_path);
+fn main() -> Result<(), LinuxI2CError> {
+    let mut verbose = false;
+    let mut args = env::args().skip(1).peekable();
+
+    if let None = args.peek() {
+        eprintln!("Usage: tiny-wetter [-v] <i2c device> <altitude>");
+        return Ok(());
+    }
+
+    if let Some(arg) = args.peek() {
+        if arg == "-v" {
+            verbose = true;
+            args.next();
+        }
+    }
+
+    let i2c_path = args.next().expect("missing i2c device");
+    let altitude = args.next().expect("missing altitude").parse().expect("invalid altitude");
+
+    let weather = read_tiny_wetter(&i2c_path)?;
+
+    if verbose {
+        println!("temperature (bmp280):  {:6.1} °C", weather.temperature_bmp280);
+        println!("temperature (si7021):  {:6.1} °C", weather.temperature_si7021);
+        println!("corrected temperature: {:6.1} °C", weather.temperature());
+        println!("relative humidity:     {:6.1} %", weather.relative_humidity);
+        println!("real pressure:         {:6.1} hPa", weather.pressure / 100.);
+        println!("pressure at sea level: {:6.1} hPa", weather.sea_level_preassure(altitude) / 100.);
+    } else {
+        println!("{:.1} {:.1} {:.1}",
+            weather.temperature(),
+            weather.relative_humidity,
+            weather.sea_level_preassure(altitude) / 100.,
+        );
+    }
+
+    Ok(())
 }
 
-fn i2c_sensors(path: &str) {
-    let i2c_device = LinuxI2CDevice::new(path, 0b1110110).unwrap();
+struct TinyWetterReading {
+    temperature_bmp280: f32,
+    temperature_si7021: f32,
+    pressure: f32,
+    relative_humidity: f32,
+}
 
-    let settings = BMP280Settings {
+impl TinyWetterReading {
+    fn temperature(&self) -> f32 {
+        (self.temperature_bmp280 + self.temperature_si7021) / 2. - 1.
+    }
+
+    fn sea_level_preassure(&self, altitude: f32) -> f32 {
+        let coef = 13f32 / 2000.;
+
+        let divisor = self.temperature() + coef * altitude + 273.15;
+        self.pressure * (1f32 - coef * altitude / divisor).powf(-5.257)
+    }
+}
+
+fn read_tiny_wetter(path: &str) -> Result<TinyWetterReading, LinuxI2CError> {
+    let bmp280_settings = BMP280Settings {
         compensation: BMP280CompensationAlgorithm::Float,
         t_sb: BMP280Timing::ms4000,
         iir_filter_coeff: BMP280FilterCoefficient::UltraHigh,
-        osrs_t: BMP280TemperatureOversampling::x2,
+        osrs_t: BMP280TemperatureOversampling::x16,
         osrs_p: BMP280PressureOversampling::UltraHighResolution,
-        power_mode: BMP280PowerMode::NormalMode,
+        power_mode: BMP280PowerMode::ForcedMode,
     };
 
-    let mut bmp280 = BMP280::new(i2c_device, settings).unwrap();
+    let i2c_device = LinuxI2CDevice::new(path, BMP280_I2C_ADDRESS)?;
+    let mut bmp280 = BMP280::new(i2c_device, bmp280_settings)?;
 
-    println!("pressure: {:6.2} kPa", bmp280.pressure_kpa().unwrap());
-    println!("temp1:    {:6.2} °C", bmp280.temperature_celsius().unwrap());
+    let i2c_device = LinuxI2CDevice::new(path, SI7021_I2C_ADDRESS)?;
+    let mut si7021 = Si7021::new(i2c_device);
 
-    let device = LinuxI2CDevice::new(path, SI7021_I2C_ADDRESS).unwrap();
-    let mut si7021 = Si7021::new(device);
-    println!("humidity: {:6.2} %", si7021.relative_humidity().unwrap());
-    println!("temp2:    {:6.2} °C", si7021.temperature_celsius().unwrap());
+
+    Ok(TinyWetterReading {
+        temperature_bmp280: bmp280.temperature_celsius()?,
+        temperature_si7021: si7021.temperature_celsius()?,
+        pressure: bmp280.pressure_kpa()? * 1000.,
+        relative_humidity: si7021.relative_humidity()?,
+    })
 }