A method of using an electrochemical device includes at least first and second electrodes; a chamber for receiving a fluid sample and defining a volume partially bounded by a first portion of the first electrode and a second portion of the second electrode, the first portion having a first characteristic for influencing an electrochemical reaction at the first portion, the second portion having a second characteristic for influencing an electrochemical reaction at the second portion, the first and second characteristics having a predetermined relationship. The method also includes receiving a fluid sample in the chamber; measuring first and second electrical outputs at least one of the first and second electrodes; and determining whether the first and second electrical outputs are related according to the predetermined relationship.