Would some kind person be able to tell me the offset angle of an Ipstar antenna.  The horizontal diameter of the dish is about 1.2 m and my rough attempts so far suggest that the angle is more than 20°.

Thanks.

You could try

https://www.satsig.net/pointing/finding-dish-offset-angle.htm

I am not sure it gives correct or accurate results but you could give it a try.  It assumes the rim of the dish is truly flat.

Best regards, Eric.

Thanks Eric.  I was hoping that someone would know the design angle but I will get around to measuring - not so good on a ladder any more.
Best regards,
John

If your antenna is anything like this:
https://www.ipstar.com/pdf/products/IPatenna.pdf

Note that the rim does not appear flat. Therefore the calculation won't work.

If you are pointed at a known satellite find out the calculated elevation angle for your location using
https://www.satsig.net/maps/satellite-tv-dish-pointing-south-east-asia.htm

Then note or mark the elevation angle on the scale. At least that marked point of the scale will then have an exact meaning for you.  Set other elevations angles relative to that mark.