I wonder if 1146 could have been a peak flow recorder. Suppose you want a record of peak rainfall. You smear chalk along the spiral. You set the cup under shelter and make sure it's level. You put in a tube that carries water collected from a surface of a certain size. The end of the tube should be near the bottom of the cup to avoid splashing.
As the water rises, it will flow out the holes along the spiral, washing away the chalk on its way down. When people ask the scientist if it rained cats and dogs last night, he checks the cup to see how much chalk was washed away.
A higher level would mean more holes as well as more pressure, so maybe it would measure the log of the flow. To be precise, the scientist would have to know the temperature of the water because that would determine viscosity.