контекст:

This procedure may be checked for proper execution
by testing the ASTM D24 Standard Reference Blacks. The
standard value and range for each, when tested by this test
method, is given in Guide D 4821. However, due to the iodine
adsorption number of carbon blacks decreasing with age
(including SRB's), the preferred technique for monitoring
proper test execution is to utilize a statistical control chart
(x-chart) to continuously monitor testing as described in
D4821.

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