There are a number of tests in the Hach LCK cuvette range that require a blank vial to be tested prior to running a sample. The value E1 on screen indicates that this value is to be subtracted from the final reading. This will also appear with some tests where the value is measured before and after the sample addition.
Camlab are able to offer both the new product and a range of services for the older units, including spares, calibration and replacement test kits, contact us below for details. Full Hach Range online at camlab