diff --git a/2-IOC-deployment.md b/2-IOC-deployment.md
index 2cd25c8823b8095bad609e46ed941e09ee1eb8a4..ad1d68fa0fb9047f200d4f2582bcceb1561eec67 100644
--- a/2-IOC-deployment.md
+++ b/2-IOC-deployment.md
@@ -115,6 +115,24 @@ configure/CONFIG:18: *** EPICS_BASE must be set in a configure/RELEASE file.  St
 ```
 </details>
 
+<details>
+<summary>what does this mean?</summary>
+
+This error message indicates that the EPICS_BASE environment variable is not defined in your configure/RELEASE file.
+
+EPICS_BASE is a mandatory environment variable that points to the location of the EPICS base installation directory. The configure/RELEASE file is used to define EPICS-related environment variables required for building an IOC.
+
+Here's an example of how to set the EPICS_BASE variable in the configure/RELEASE file:
+
+```
+EPICS_BASE=/path/to/epics/base
+```
+
+where "/path/to/epics/base" points to your EPICS base installation directory.
+
+Once you have set the EPICS_BASE variable in the configure/RELEASE file, try building your IOC again and the error should be resolved.
+</details>
+
 ### 2.5 Resolve build error #1
 
 Modify **configure/RELEASE** so that ``EPICS_BASE`` is defined.