Update customisation.md

docs/customisation.md

@@ -237,10 +237,17 @@ NOTE: This feature is quite slow and so may need a higher performance machine.
 
 This can help to slightly improve the plan for tariffs like Agile but can make it worse in some fixed rate tariffs which you want to force export late.
 
-**switch.predbat_calculate_secondary_order** (_expert_mode_) When True import slots of the same value are sorted by export price and export slots of
-the same value are sorted by import price. When False slots of the same price are sorted by time.
+**switch.calculate_import_low_export** (_expert_mode_) When True import slots of the same value are sorted by export price. 
+When False they are sorted just by price and then time. The default is True.
 
-Turning this switch off can be used to push export as late as possible when you have a fixed price export tariff.
+By default with this option enabled if there are multiple charge slots of the same price Predbat will try to charge when the export rates are lowest
+thus leaving the higher export slots available.
+
+**switch.calculate_export_low_import** (_expert_mode_) When True export slots of the same value are sorted by import price. 
+When False they are sorted just by price and then time. The default is False.
+
+By default with this option disabled the latest export slot of the same value will be picked, this is useful for fixed price export tariffs where
+you want to export as late in the day as you can.
 
 ## Battery margins and metrics options