diff --git a/tfmkt/utils.py b/tfmkt/utils.py
index ab39f99..8ba3f4e 100644
--- a/tfmkt/utils.py
+++ b/tfmkt/utils.py
@@ -25,9 +25,6 @@ def background_position_in_px_to_minute(px_x: int, px_y: int) -> int:
     :rtype: int
     """
 
-    if abs(px_y) > 36*12: # no data available
-        return -1
-        
     n = 10 # number of columns in the matrix
     m = 13 # number of rows in the matrix
     h = 36 # size of the chronometer square in pixels
@@ -40,6 +37,9 @@ def background_position_in_px_to_minute(px_x: int, px_y: int) -> int:
         for a in range(1, m)
     ]
 
+    if abs(px_y) > h*(m - 1 - y_offset): # no data available
+        return -1
+
     x = abs(px_x) / h
     assert x.is_integer()
     x = int(x) + x_offset