diff --git a/Days/day15.md b/Days/day15.md
index c74e559..3b0180d 100644
--- a/Days/day15.md
+++ b/Days/day15.md
@@ -87,6 +87,27 @@ If you have a long complex configuration file and you want or need to find somet
 
 If you are like me and you use that `clear` command a lot then you might miss some of the commands previously ran, we can use `history` to find out all those commands we have run prior. `history -c` will remove the history. 
 
+When you run `history` and you would like to pick a specific command you can use `!3` to choose the 3rd command in the list. 
+
+You are also able to use `history | grep "Command` to search for something specific. 
+
+On servers to trace back when was a command executed, it can be useful to append the date and time to each command in the history file.
+
+The following system variable controls this behaviour:
+```
+HISTTIMEFORMAT="%d-%m-%Y %T "
+```
+You can easily add to your bash_profile:
+```
+echo 'export HISTTIMEFORMAT="%d-%m-%Y %T "' >> ~/.bash_profile
+```
+So as useful to allow the history file grow bigger:
+
+```
+echo 'export HISTSIZE=100000' >> ~/.bash_profile
+echo 'export HISTFILESIZE=10000000' >> ~/.bash_profile
+```
+
 ![](Images/Day15_Linux21.png)
 
 Need to change your password? `passwd` is going allow us to change our password. Note that when you add your password in like this when it is hidden it will not be shown in `history` however if your command has `-p PASSWORD` then this will be visible in your `history`. 
diff --git a/README.md b/README.md
index 1923e49..b1518f8 100644
--- a/README.md
+++ b/README.md
@@ -43,8 +43,8 @@ This will not cover all things DevOps but it will cover the areas that I feel wi
 ### Understand Networking
 
 - [✔️] 🌐 21 > [The Big Picture - DevOps and Networking](Days/day21.md)
-- [🚧] 🌐 22 > [](Days/day22.md)
-- [] 🌐 23 > [](Days/day23.md)
+- [✔️] 🌐 22 > [The OSI Model - The 7 Layers](Days/day22.md)
+- [🚧] 🌐 23 > [](Days/day23.md)
 - [] 🌐 24 > [](Days/day24.md)
 - [] 🌐 25 > [](Days/day25.md)
 - [] 🌐 26 > [](Days/day26.md)