The Sherwood Model 41O has been accepted world wide as the standard manual Flame Photometer. It can measure Sodium, Potassium, Lithium, and with interchangeable filters, Calcium and Barium and is used in laboratories serving a very wide variety of industries. In the clinical field the addition of a Lineariser module enables direct reading of Sodium as well as Potassium and Lithium values.

The Sherwood Model 420 has been developed from the Model 410 with the objective of improving the productivity and analytical performance of the laboratory when measuring Sodium and Potassium. The biggest improvement is dual channel operation allowing both Sodium and Potassium to be measured and displayed simultaneously. The Model 420 retains the heart of the Model 410 as described above but now adds a new auto flame optimisation and sophisticated software to achieve much enhanced operation.