Update README.md

README.md

@@ -21,15 +21,15 @@ More information about the installation process can be found on the [documentati
 
 ## ITU-P Recommendations implemented:
 The following ITU-P Recommendations are implemented in ITU-Rpy
-* **ITU-P R.453-12:** The radio refractive index: its formula and refractivity data
-* **ITU-P R.618-12:** Propagation data and prediction methods required for the design of Earth-space telecommunication systems
+* **ITU-P R.453-13:** The radio refractive index: its formula and refractivity data
+* **ITU-P R.618-13:** Propagation data and prediction methods required for the design of Earth-space telecommunication systems
 * **ITU-P R.676-11:** Attenuation by atmospheric gases
-* **ITU-P R.835-12:** Reference Standard Atmospheres
-* **ITU-P R.836-5:** Water vapour: surface density and total columnar content
-* **ITU-P R.837-6:** Characteristics of precipitation for propagation modelling
+* **ITU-P R.835-6:** Reference Standard Atmospheres
+* **ITU-P R.836-6:** Water vapour: surface density and total columnar content
+* **ITU-P R.837-7:** Characteristics of precipitation for propagation modelling
 * **ITU-P R.838-3:** Specific attenuation model for rain for use in prediction methods
 * **ITU-P R.839-4:** Rain height model for prediction methods.
-* **ITU-P R.840-6:** Attenuation due to clouds and fog 
+* **ITU-P R.840-7:** Attenuation due to clouds and fog 
 * **ITU-P R.1144-7:** Interpolation methods for the geophysical properties used to compute propagation effects 
 * **ITU-P R.1511-1:** Topography for Earth-to-space propagation modelling
 * **ITU-P R.1853-1:** Tropospheric attenuation time series synthesis
@@ -41,12 +41,11 @@ The individual models can be accessed using the `itur.models` package.
 The following code example shows the usage of ITU-Rpy. More examples can be found in the [examples folder](https://github.com/iportillo/ITU-Rpy/tree/master/examples).
 ```python
 import itur
-from astropy import units as u
 
-f = 22.5 * u.GHz    # Link frequency
-D = 1 * u.m       # Size of the receiver antenna
-el = 60           # Elevation angle constant of 60 degrees
-p = 3             # Percentage of time that attenuation values are exceeded.
+f = 22.5 * itur.u.GHz    # Link frequency
+D = 1 * itur.u.m         # Size of the receiver antenna
+el = 60                  # Elevation angle constant of 60 degrees
+p = 3                    # Percentage of time that attenuation values are exceeded.
 
 # Generate a regular grid latitude and longitude points with 1 degrees resolution	
 lat, lon = itur.utils.regular_lat_lon_grid()