diff --git a/Pasted image 20210719000516.png b/Pasted image 20210719000516.png
new file mode 100644
index 000000000..5c02da3e5
Binary files /dev/null and b/Pasted image 20210719000516.png differ
diff --git a/Pasted image 20210719000525.png b/Pasted image 20210719000525.png
new file mode 100644
index 000000000..2ce5e5423
Binary files /dev/null and b/Pasted image 20210719000525.png differ
diff --git a/stpa handbook.md b/stpa handbook.md
index b8598873d..18b32df4d 100644
--- a/stpa handbook.md	
+++ b/stpa handbook.md	
@@ -38,4 +38,10 @@ Definition of [[system]]:
 
 The heart of STPA: the control loop. 
 
-![[Pasted image 20210718234343.png]]
\ No newline at end of file
+![[Pasted image 20210718234343.png]]
+
+Refining control structures:
+
+![[Pasted image 20210719000525.png]]
+
+![[Pasted image 20210719000516.png]]
\ No newline at end of file