diff --git a/src/main.py b/src/main.py
index ba39256..1992481 100644
--- a/src/main.py
+++ b/src/main.py
@@ -110,11 +110,21 @@ def deduplicate_instruments_from_layers(layers):
         lasers.append(instruments["laser_system"])
         chambers.append(instruments["deposition_chamber"])
         rheeds.append(instruments["rheed_system"])
+        ded_lasers = list( set( lasers ) )
+        ded_chambers = list( set( chambers ) )
+        ded_rheeds = list( set( rheeds ) )
+        elegant_list = [ ded_lasers, ded_chambers, ded_rheeds]
+    if not all([ len(i) == 1 for i in elegant_list ]):
+        print("Warning: different instruments have been used for different layers - which is currently not allowed.")
+        print("Selecting the first occurence for every category...")
     instruments_used_dict = {
-        "laser_system": list( set( lasers ) ),
-        "deposition_chamber": list( set( chambers ) ),
-        "rheed_system" : list( set( rheeds ) ),
+        "laser_system": ded_lasers[0],
+        "deposition_chamber": ded_chambers[0],
+        "rheed_system": ded_rheeds[0],
     }
+    return instruments_used_dict
+
+        
     # lasers = { f"layer_{lyr.layer_number}": lyr.laser_system for lyr in layers }
     # chambers = { f"layer_{lyr.layer_number}": lyr.deposition_chamber for lyr in layers }
     # rheeds = { f"layer_{lyr.layer_number}": lyr.rheed_system for lyr in layers }