Triple Aquastat from Honeywel (L6081A)

I bought a house recently that had Honeywell boiler in it. That boiler has L6081 A Triple Aquastat. It has "LOW", "HIGH" and "DIFF" controls. My question is, what is the purpose of that "DIFF" control with the marks from 10 to 25? Any help is greatly appreciated
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ARTHUR wrote:

The LOW limit controls the circulator pump. The DIFF is the differential between ON and OFF points on the LOW dial. A larger DIFF setting will prevent the circ pump from cycling on and off frequently.
The HIGH limit controls the boiler max temp. Its differential is fixed.
Jim
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