Hitachi ZA3000 Series Instruction Manual page 334

The in-furnace addition method is a method of preparing and
measuring mixed samples (not mixed equally) in cuvettes by
preparing standard solutions and unknown samples separately
and adding each sample individually.
If mixing of unknown and standard samples in the furnace is
inadequate due to a reason such as high sample viscosity, "5.1.3
Standard Addition Method (ex-furnace addition)" should be used.
(1) Starting from the Method window, make entries in the
[Measurement Mode] window, [Elements] window,
[Instrument Setup] window and [Analytical Condition]
window. For these entries, refer to Section 3.
(2) Click the [Standards Table] button to display the Standards
Table window (Fig. 5-3).
Fig. 5-3 Standards Table Window
(3) In [Determination Mode], select [STD Add.], and in [Order],
select [Linear].
5 - 5
5.1.2