diff --git a/src/aarecommon/math/find_xtal.py b/src/aarecommon/math/find_xtal.py
index e9147ca..699382d 100644
--- a/src/aarecommon/math/find_xtal.py
+++ b/src/aarecommon/math/find_xtal.py
@@ -271,13 +271,17 @@ def get_best_res(result_list: list):
 
 
 def get_res_of_image_number(
-    result_list: list[ScanResultImagesInner], image_index: int | None
+    result_list: list[ScanResultImagesInner], image_number: int | None
 ) -> float | None:
-    if image_index is None or image_index >= len(result_list):
+    if image_number is None:
         return None
-    image = result_list[image_index]
-    logger.info(f"Resolution estimage for selected gridscan image (# {image_index}): {image.res}")
-    return image.res
+    for image in result_list:
+        if image.number == image_number:
+            logger.info(
+                f"Resolution estimage for selected gridscan image (# {image_number}): {image.res}"
+            )
+            return image.res
+    return None
 
 
 def com_nan_check(com):