GSM FlexJet z-safe sensor

We have GSM2 with FlexJet heads (an older one). There are 7 sensor amplifiers (with LED indicators) for touchdown detection and one for z-safe detection which is of a different type (with numeric LED indicator). I can't find anywhere what the right number range is. All documents I can find deal with a different head type where all 8 amplifiers have LED bargraph indicator types. Can anybody help me there?

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