Yes. You can set admission number as per the school register number. In Klearskool, the first admission number you enter should be your school register number and then from next admission,  Klearskool will handle the admission number automatically ( if auto increment option is enabled in General settings).

Suppose the register number is AF67, Then during the first admission, give this admission number. From the next admission on-wards, the number will be incremented (you have to enable the auto increment admission number option in general settings section in Settings module for this to work)

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