diff --git a/Master-Server-API.md b/Master-Server-API.md
index 28789ac..ccfb73b 100644
--- a/Master-Server-API.md
+++ b/Master-Server-API.md
@@ -41,7 +41,7 @@ curl "http://localhost:9333/dir/lookup?volumeId=3&collection=turbo"
 
 ### Force garbage collection
 
-If your system has many deletions, the deleted file's disk space will not be synchronously re-claimed. There is a background job to check volume disk usage. If empty space is more than the threshold, default to 0.3, the vacuum job will make the volume readonly, create a new volume with only existing files, and switch on the new volume. If you are impatient or doing some testing, vacuum the unused spaces this way.
+If your system has many deletions, the deleted file's disk space will not be synchronously re-claimed. There is a background job to check volume disk usage. If empty space is more than the threshold, default to 0.3 which is 30%, the vacuum job will make the volume readonly, create a new volume with only existing files, and switch on the new volume. If you are impatient or doing some testing, vacuum the unused spaces this way.
 
 ```bash
 curl "http://localhost:9333/vol/vacuum"