diff --git a/.DS_Store b/.DS_Store
index 331a20d..1e014ef 100644
Binary files a/.DS_Store and b/.DS_Store differ
diff --git a/pyatmos/.DS_Store b/pyatmos/.DS_Store
index d752f51..dfca1f5 100644
Binary files a/pyatmos/.DS_Store and b/pyatmos/.DS_Store differ
diff --git a/pyatmos/utils/Const.py b/pyatmos/utils/Const.py
index 135efca..847df08 100644
--- a/pyatmos/utils/Const.py
+++ b/pyatmos/utils/Const.py
@@ -15,12 +15,10 @@ fourpi = 4*np.pi
 degrad = pi / 180
 al10 = np.log(10)
 
-# AVOGAD is Avogadro's number in mks units (molecules/kmol)
-avogad = 6.02257e26
+avogad = 6.02257e26 # The Avogadro's number in mks units (molecules/kmol)
 pivo2 = 1.5707963
 pivo4 = 1.5707963  
 
-# RSTAR is the universal gas-constant in mks units (joules/K/kmol)
-rstar = 8314.32
+rstar = 8314.32 # The universal gas-constant in mks units (joules/K/kmol)
 
 x = np.arange(0.5,48)/24
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diff --git a/pyatmos/utils/data_download.py b/pyatmos/utils/data_download.py
new file mode 100644
index 0000000..08c84c6
--- /dev/null
+++ b/pyatmos/utils/data_download.py
@@ -0,0 +1,58 @@
+from datetime import datetime,timedelta
+from os import path,makedirs,remove
+from pathlib import Path
+
+from .try_download import wget_download 
+
+def download_iers(out_days=7,dir_to=None):
+    """
+    Download or update the Earth Orientation Parameters(EOP) file and Leap Second file from IERS
+
+    Usage: 
+        >>> dir_to,dir_eop_file,dir_leapsecond_file = download_iers()
+    Inputs: 
+        out_days -> [int, optional, default = 7] Updating cycle of the IERS files
+        dir_to   -> [str, optional, default = None] Directory for storing EOP file
+    Outputs: 
+        dir_to -> [str] Directory of the IERS files
+        dir_eop_file -> [str] Path of the EOP file
+        dir_leapsecond_file -> [str] Path of the Leap Second file
+    """
+    if dir_to is None:
+        home = str(Path.home())
+        dir_to = home + '/src/iers/'
+    
+    eop_file = 'finals2000A.all'
+    leapsecond_file = 'Leap_Second.dat'
+    dir_eop_file = dir_to + eop_file
+    dir_leapsecond_file = dir_to + leapsecond_file
+
+    url_eop = 'https://datacenter.iers.org/products/eop/rapid/standard/finals2000A.all'
+    url_leapsecond = 'https://hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat'
+
+    if not path.exists(dir_to): makedirs(dir_to)
+    if not path.exists(dir_eop_file):
+        desc = "Downloading the latest EOP file '{:s}' from IERS".format(eop_file)
+        wget_out = wget_download(url_eop,dir_eop_file,desc)
+    else:
+        modified_time = datetime.fromtimestamp(path.getmtime(dir_eop_file))
+        if datetime.now() > modified_time + timedelta(days=out_days):
+            remove(dir_eop_file)
+            desc = "Updating the EOP file '{:s}' from IERS".format(eop_file)
+            wget_out = wget_download(url_eop,dir_eop_file,desc)
+        else:
+            print("The EOP file '{:s}' in {:s} is already the latest.".format(eop_file,dir_to)) 
+
+    if not path.exists(dir_leapsecond_file):
+        desc = "Downloading the latest Leap Second file '{:s}' from IERS".format(leapsecond_file)
+        wget_out = wget_download(url_leapsecond,dir_leapsecond_file,desc)
+    else:
+        modified_time = datetime.fromtimestamp(path.getmtime(dir_leapsecond_file))
+        if datetime.now() > modified_time + timedelta(days=out_days):
+            remove(dir_leapsecond_file)
+            desc = "Updating the Leap Second file '{:s}' from IERS".format(leapsecond_file)
+            wget_out = wget_download(url_leapsecond,dir_leapsecond_file,desc)
+        else:
+            print("The Leap Second file '{:s}' in {:s} is already the latest.".format(leapsecond_file,dir_to))        
+
+    return dir_to,dir_eop_file,dir_leapsecond_file    
\ No newline at end of file