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The number of significant figures of a quantity value implies specific requirements for the quantities (masses and volumes) to be measured, as detailed in the section on ‘Quantities’ in the Ph. Eur. General Notices.
In tests with numerical limits and assays, the quantity stated to be taken for examination corresponds to the quantity used during development of the analytical procedure. The amount actually used may deviate by not more than 10 per cent from the stated quantity. In any case, the amount used is accurately measured and the result of the test is calculated from this exact quantity.
In tests where the limit is not numerical, which usually depend instead upon comparison with the behaviour of a reference substance in the same conditions, the stated quantity is taken for examination.
Reagents are used in the prescribed amounts.