From fe6252c268f51658e5de6e017cf6985e1f1f0e85 Mon Sep 17 00:00:00 2001
From: Ryan Howard <ryan.howard@opentrons.com>
Date: Wed, 7 Aug 2024 10:43:35 -0400
Subject: [PATCH] fix(api): made a mistake in math when i removed the isclose
 check (#15913)

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# Overview
Should have realized it was wrong when I had to change the test
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Co-authored-by: caila-marashaj <caila.marashaj@opentrons.com>
---
 api/src/opentrons/hardware_control/ot3api.py         | 7 +++++--
 api/tests/opentrons/hardware_control/test_ot3_api.py | 4 ++--
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/api/src/opentrons/hardware_control/ot3api.py b/api/src/opentrons/hardware_control/ot3api.py
index 4f0cf262775..5f9c9840834 100644
--- a/api/src/opentrons/hardware_control/ot3api.py
+++ b/api/src/opentrons/hardware_control/ot3api.py
@@ -2714,7 +2714,10 @@ async def liquid_probe(
 
         error: Optional[PipetteLiquidNotFoundError] = None
         pos = await self.gantry_position(checked_mount, refresh=True)
-        while (probe_start_pos.z - pos.z) < max_z_dist:
+        #  probe_start_pos.z + z_distance of pass - pos.z should be < max_z_dist
+        # due to rounding errors this can get caught in an infinite loop when the distance is almost equal
+        # so we check to see if they're within 0.01 which is 1/5th the minimum movement distance from move_utils.py
+        while (probe_start_pos.z - pos.z) < (max_z_dist + 0.01):
             # safe distance so we don't accidentally aspirate liquid if we're already close to liquid
             safe_plunger_pos = top_types.Point(
                 pos.x, pos.y, pos.z + probe_safe_reset_mm
@@ -2724,7 +2727,7 @@ async def liquid_probe(
                 pos.x, pos.y, pos.z + probe_pass_z_offset_mm
             )
             max_z_time = (
-                max_z_dist - (probe_start_pos.z - safe_plunger_pos.z)
+                max_z_dist - probe_start_pos.z + pass_start_pos.z
             ) / probe_settings.mount_speed
             p_travel_required_for_z = max_z_time * probe_settings.plunger_speed
             p_pass_travel = min(p_travel_required_for_z, p_working_mm)
diff --git a/api/tests/opentrons/hardware_control/test_ot3_api.py b/api/tests/opentrons/hardware_control/test_ot3_api.py
index 21ab1ad8ef9..190f8841c13 100644
--- a/api/tests/opentrons/hardware_control/test_ot3_api.py
+++ b/api/tests/opentrons/hardware_control/test_ot3_api.py
@@ -838,7 +838,7 @@ async def test_liquid_probe(
         mock_move_to_plunger_bottom.call_count == 2
         mock_liquid_probe.assert_called_once_with(
             mount,
-            52,
+            46,
             fake_settings_aspirate.mount_speed,
             (fake_settings_aspirate.plunger_speed * -1),
             fake_settings_aspirate.sensor_threshold_pascals,
@@ -990,7 +990,7 @@ async def _fake_pos_update_and_raise(
             OT3Mount.LEFT, fake_max_z_dist, fake_settings_aspirate
         )
     # assert that it went through 4 passes and then prepared to aspirate
-    assert mock_move_to_plunger_bottom.call_count == 5
+    assert mock_move_to_plunger_bottom.call_count == 4
 
 
 @pytest.mark.parametrize(