diff --git a/src/dopt_sensor_anomalies/detection.py b/src/dopt_sensor_anomalies/detection.py
index f74d133..1a2b981 100644
--- a/src/dopt_sensor_anomalies/detection.py
+++ b/src/dopt_sensor_anomalies/detection.py
@@ -140,9 +140,9 @@ def measure_length(
             f"expected value: count = {num_contours}, expected = {const.NUM_VALID_ELECTRODES}"
         )
 
-    x_min = min(np.min(c[:, 0, 0]) for c in filtered_cnts) - 20
+    x_min = max(min(np.min(c[:, 0, 0]) for c in filtered_cnts) - 20, 0)
     x_max = max(np.max(c[:, 0, 0]) for c in filtered_cnts) + 20
-    y_min = min(np.min(c[:, 0, 1]) for c in filtered_cnts) - 20
+    y_min = max(min(np.min(c[:, 0, 1]) for c in filtered_cnts) - 20, 0)
     y_max = max(np.max(c[:, 0, 1]) for c in filtered_cnts) + 20
 
     rightmost_x_third = max(filtered_cnts[2][:, 0, 0])