Thanks! And yes a typo should read 2900 rpm thanks for picking that up.
How do i find out/work out the port ratio?

Hi everyone, I am a new member and I am hoping to find out more about a Crompton Air Raid siren that was used in Tamworth NSW Australia in WW2. It still works. I am attaching a picture. I am a volunteer cataloguer at the Tamworth Powerstation Museum and this is part of the collection. Thanks! From t...