measure evaporation from previous trial so that liquid-tracker can up…

…date using it's aspirate method

hardware-testing/hardware_testing/gravimetric/execute.py

@@ -42,7 +42,7 @@
 
 _MEASUREMENTS: List[Tuple[str, MeasurementData]] = list()
 
-_STARTING_GRAMS: Optional[MeasurementData] = None
+_PREV_TRIAL_GRAMS: Optional[MeasurementData] = None
 
 
 def _generate_callbacks_for_trial(
@@ -329,7 +329,7 @@ def _run_trial(
     scale_delay: int = DELAY_FOR_MEASUREMENT,
     measure_height: float = 50,
 ) -> Tuple[float, MeasurementData, float, MeasurementData]:
-    global _STARTING_GRAMS
+    global _PREV_TRIAL_GRAMS
     pipetting_callbacks = _generate_callbacks_for_trial(
         recorder, volume, channel, trial, blank
     )
@@ -369,16 +369,15 @@ def _record_measurement_and_store(m_type: MeasurementType) -> MeasurementData:
     pipette.move_to(well.top(measure_height).move(channel_offset))
     m_data_init = _record_measurement_and_store(MeasurementType.INIT)
     print(f"\tinitial grams: {m_data_init.grams_average} g")
-    if _STARTING_GRAMS is None:
-        _STARTING_GRAMS = m_data_init
-    else:
+    if _PREV_TRIAL_GRAMS is not None:
         _evaporation_loss_ul = abs(
-            calculate_change_in_volume(_STARTING_GRAMS, m_data_init)
+            calculate_change_in_volume(_PREV_TRIAL_GRAMS, m_data_init)
         )
-        print(f"calculated {_evaporation_loss_ul} ul has evaporated during the test")
+        print(f"{_evaporation_loss_ul} ul evaporated since last trial")
         liquid_tracker.update_affected_wells(
             well, aspirate=_evaporation_loss_ul, channels=1
         )
+    _PREV_TRIAL_GRAMS = m_data_init
 
     # RUN ASPIRATE
     aspirate_with_liquid_class(