diff --git a/pico-cp/__pycache__/code.cpython-312.pyc b/pico-cp/__pycache__/code.cpython-312.pyc
index 736f663..19a9796 100644
Binary files a/pico-cp/__pycache__/code.cpython-312.pyc and b/pico-cp/__pycache__/code.cpython-312.pyc differ
diff --git a/pico-cp/code.py b/pico-cp/code.py
index 3b42d0f..835bc85 100644
--- a/pico-cp/code.py
+++ b/pico-cp/code.py
@@ -357,10 +357,16 @@ class App:
         self.bpm, self.lanes = parse_program(prog)
         self.master = self.lanes[0]
         self._reset_clock(); self.draw_bpm(); self.draw_status(); self.build_grid()
+    def _lane_dur(self, L):
+        beat = 60_000_000_000 / self.bpm
+        if L['poly']:                                   # ~ polymeter: fit this lane's whole cycle into lane 1's bar
+            m = self.lanes[0]; master_bar = beat * (m['steps'] // m['sub'])
+            return int(master_bar / L['steps'])
+        return int(beat / L['sub'])                     # straight: a step = one beat / subdivision
     def _reset_clock(self):
         now = time.monotonic_ns()
         for L in self.lanes:
-            L['next'] = now; L['step'] = -1; L['dur'] = int(60_000_000_000 / self.bpm / L['sub'])
+            L['next'] = now; L['step'] = -1; L['dur'] = self._lane_dur(L)
 
     # ---------- audio + light ----------
     def click(self, level):
@@ -388,7 +394,7 @@ class App:
         v = max(30, min(300, v))
         if v != self.bpm:
             self.bpm = v
-            for L in self.lanes: L['dur'] = int(60_000_000_000 / self.bpm / L['sub'])
+            for L in self.lanes: L['dur'] = self._lane_dur(L)
             self.draw_bpm()
     def goto(self, i):
         was = self.running; self.load(i); self._label("play")