diff --git a/klippy/clocksync.py b/klippy/clocksync.py
index ce5e42a2..65c3face 100644
--- a/klippy/clocksync.py
+++ b/klippy/clocksync.py
@@ -165,6 +165,7 @@ class SecondarySync(ClockSync):
         ClockSync.__init__(self, reactor)
         self.main_sync = main_sync
         self.clock_adj = (0., 1.)
+        self.last_sync_time = 0.
     def connect(self, serial):
         ClockSync.connect(self, serial)
         self.clock_adj = (0., self.mcu_freq)
@@ -195,18 +196,25 @@ class SecondarySync(ClockSync):
         adjusted_offset, adjusted_freq = self.clock_adj
         return "%s adj=%d" % (ClockSync.stats(self, eventtime), adjusted_freq)
     def calibrate_clock(self, print_time, eventtime):
+        # Calculate: est_print_time = main_sync.estimatated_print_time()
         ser_time, ser_clock, ser_freq = self.main_sync.clock_est
         main_mcu_freq = self.main_sync.mcu_freq
-
-        main_clock = (eventtime - ser_time) * ser_freq + ser_clock
-        print_time = max(print_time, main_clock / main_mcu_freq)
-        main_sync_clock = (print_time + 4.) * main_mcu_freq
-        sync_time = ser_time + (main_sync_clock - ser_clock) / ser_freq
-
-        print_clock = self.print_time_to_clock(print_time)
-        sync_clock = self.get_clock(sync_time)
-        adjusted_freq = .25 * (sync_clock - print_clock)
-        adjusted_offset = print_time - print_clock / adjusted_freq
-
+        est_main_clock = (eventtime - ser_time) * ser_freq + ser_clock
+        est_print_time = est_main_clock / main_mcu_freq
+        # Determine sync1_print_time and sync2_print_time
+        sync1_print_time = max(print_time, est_print_time)
+        sync2_print_time = max(sync1_print_time + 4., self.last_sync_time,
+                               2.5 * (print_time - est_print_time))
+        # Calc sync2_sys_time (inverse of main_sync.estimatated_print_time)
+        sync2_main_clock = sync2_print_time * main_mcu_freq
+        sync2_sys_time = ser_time + (sync2_main_clock - ser_clock) / ser_freq
+        # Adjust freq so estimated print_time will match at sync2_print_time
+        sync1_clock = self.print_time_to_clock(sync1_print_time)
+        sync2_clock = self.get_clock(sync2_sys_time)
+        adjusted_freq = ((sync2_clock - sync1_clock)
+                         / (sync2_print_time - sync1_print_time))
+        adjusted_offset = sync1_print_time - sync1_clock / adjusted_freq
+        # Apply new values
         self.clock_adj = (adjusted_offset, adjusted_freq)
+        self.last_sync_time = sync2_print_time
         return self.clock_adj