Problem creating a large, accurately scaled PDF output for plotting

I am working on a large site and plant installation and would like to plot an A1 drawing of the site at 1:500 scale.

I have created an oversize A1 paper size (84.1x64.4cm) to allow 2.5cm margins on all sides and still have a full size plot at 84.1x59.4cm. I have placed a scale bar on the drawing to check the accuracy of the output.

The pdf which has been created is 29.7x21cm, ie A4 size, despite the oversize. These screen shots below show the printer dialogue box before printing and the Adobe Acrobat document properties dialogue box once the print has been saved as a pdf. Scaling the pdf using the Acrobat measure tool with a scale of 1:500, not surprisingly, gives the wrong answer.

How can I get Rhino for Mac to control the paper output size correctly to A1?

For comparison, this screen shot shows the same drawing prepared using Microstation and the Page Size is 84x59.3cm, ie A1.

Sorted! Select Paper Handling and set “Scale to fit paper size” OFF. Doh!
Paper Handling - Scale to fit paper size OFF.pdf (239.1 KB)