diff --git a/README.md b/README.md
index b0ba360..a0c7c15 100644
--- a/README.md
+++ b/README.md
@@ -68,6 +68,7 @@ Use shorter values for the _duration_ and _shard duration_ if you want to. (The
 
 ```
 python readdata.py SYMBOL --start_date YYYY-MM-DD --end_date YYYY-MM-DD --do_not_write
+python readdata.py SYMBOL --start_date -2 --end_date -1 --do_not_write
 ```
 
 _SYMBOL_ has to be a Nasdaq Data Link ticker symbol. You can find the symbol in the upper right corner of the webpage that is displaying that symbol's data. 
@@ -85,11 +86,23 @@ for a help page
 
 Options starting with a _-_ or _--_ are optional and can be omitted.
 
-If `--start_date` and/or `--end_date` are omitted, the current day will be taken.
+If `--start_date` and/or `--end_date` are omitted, the current day will be taken. If a negative offset (e.g. `-1`) is given, the current date minus that number of days will be taken (e.g. -1 day)
 
 If `--do_not_write` is given, no values are written to the database
 
+#### Run via periodically via cron
 
+If you want to run this script periodically via cron, you can call the wrapper script **cronscript.sh** (rename the provided `cronscript.sh.example` to `cronscript.sh` so that local changes will not be overwritten with next git pull).
+
+8. Set execute permissions for the script: `chmod ug+x cronscript.sh`
+9. Call `crontab -e` to edit the cron table (crontab), e.g.:
+
+```
+# m h  dom mon dow   command
+0 1 1 * * /home/pi/src/nasdaq/cronscript.sh
+```
+This will run the command at 01:00h local time on every first day of every month. Edit the path to the script to wherever you put it. 
+The script assumes you have a Python virtual environment created with `python3 -m venv venv` in the same directory where you checked out the repository. The script will activate the virtual environment, call the Python interpreter with the script and will deactivate the virtual environment then.
 
 ### Files and data created
 
@@ -120,4 +133,9 @@ In the current implementation, the timestamp will always be at 0:00 local time a
 
 ## History
 
-* 21-Jun-2021: made repository public
+* 24-Jun-2021
+  * added possibilty to use offsets for the `start_date` and `end_date` parameters. You can now use `--start_date -2` to set the start date to the current date - 2 days.
+  * added example file _cronscript.sh.example_ to run this script in a Python virtual environment via cron
+
+* 21-Jun-2021
+  * made repository public
diff --git a/cronscript.sh.example b/cronscript.sh.example
new file mode 100644
index 0000000..893259f
--- /dev/null
+++ b/cronscript.sh.example
@@ -0,0 +1,7 @@
+#!/bin/bash
+SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )"
+cd $SCRIPT_DIR
+source venv/bin/activate
+python readdata.py OPEC/ORB --start_date -1
+python readdata.py BOE/XUDLERD --start_date -2
+deactivate
\ No newline at end of file
diff --git a/readdata.py b/readdata.py
index 3c32d19..b6a03ef 100644
--- a/readdata.py
+++ b/readdata.py
@@ -5,7 +5,7 @@
 import nasdaqdatalink
 from dotenv import load_dotenv
 from argparse import ArgumentParser
-from datetime import datetime
+from datetime import datetime, timedelta
 from influx18 import *
 
 def main():
@@ -32,9 +32,9 @@ def main():
     parser.add_argument("symbol", 
                         help="Ticker symbol (==Nasdaq Data Link Code), e.g. OPEC/ORB for OPEC Crude Oil)")
     parser.add_argument("-sd", "--start_date", 
-                        help="start date for the values to be received. Format: 'YYYY-MM-DD'")
+                        help="start date for the values to be received. Format: 'YYYY-MM-DD' or a negative offset (e.g. -1 = -1 day)")
     parser.add_argument("-ed", "--end_date", 
-                        help="end date for the values to be received. Format: 'YYYY-MM-DD'")
+                        help="end date for the values to be received. Format: 'YYYY-MM-DD' or a negative offset (e.g. -1 = -1 day)")
     parser.add_argument("-dnw", "--do_not_write", action='store_true',
                         help="do not write values to database")
 
@@ -51,17 +51,26 @@ def main():
     # get start and end date
     # first get the current date
     utcnow = datetime.utcnow()
-    start_date = utcnow.strftime("%Y-%m-%d")
-    end_date = utcnow.strftime("%Y-%m-%d")
-    data_link_log.debug(f"start_date (calculated): {start_date}")
-    data_link_log.debug(f"end_date (calculated): {end_date}")
 
     if args.start_date:
-        start_date = args.start_date
-    data_link_log.debug(f"start_date (set): {start_date}")
+        if str(args.start_date).startswith("-"):
+            start_date_ts = utcnow + timedelta(days=int(args.start_date))
+            start_date = start_date_ts.strftime("%Y-%m-%d")
+        else:
+            start_date = args.start_date
+    else:
+        start_date = utcnow.strftime("%Y-%m-%d")
+    data_link_log.debug(f"start_date: {start_date}")
+
     if args.end_date:
-        end_date = args.end_date
-    data_link_log.debug(f"end_date (set): {end_date}")
+        if str(args.end_date).startswith("-"):
+            end_date_ts = utcnow + timedelta(days=int(args.end_date))
+            end_date = end_date_ts.strftime("%Y-%m-%d")
+        else:
+            end_date = args.end_date
+    else:
+        end_date = utcnow.strftime("%Y-%m-%d")
+    data_link_log.debug(f"end_date: {end_date}")
 
     # read the data
     data = nasdaqdatalink.Dataset(args.symbol).data(params={ 'start_date':start_date, 'end_date':end_date})