The number of HOT cruises that can be measured with one substandard batch varies depending on the frequency of substandard measurement during a run. The frequency of measuring a substandard has varied since they were first measured during the HOT-24 salinity session. Initially, substandard measurements were used for comparison between Minisal and Autosal 8400A. Starting with HOT-27, substandards were measured about every 24 salinity samples on Autosal 8400A and continued until HOT-38. From HOT-39 onward, substandards were measured to provide a baseline measurement in case the Autosal drifted.

The frequency of substandard measurements varied with the Autosal operator, and thus determined the life span of the substandard batch. While most operators measured a substandard every 15-30 samples, the extreme cases have been a maximum at every 152 samples, and a minimum at every 6 samples. While substandard batches #6-9 lasted for about six measurement runs, batches #26-28 were depleted quickly, after only two or three measurement runs (see Figure 5B). We recommend measuring a substandard after every sample case (which holds 24 salinity sample bottles). Since we draw water samples from all 24 Niskin bottles during the first couple casts for HOT cruises, we eliminate confusion and are able to maintain consistent substandard batch life spans.

When looking back at suspicious data, knowing operator habits may help determine causes for systematic problems, errors, or differences in the salinity data from specific cruises (see Section 1.2).

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