Attached Canvas Scale different on Offset Plane

[CoastLineModels]

I have a Scanned Drawing I would like to make a 3D model from so I have attached canvas for front and side elevations on the default right and front planes and scaled them to correct size. I now want to add a back elevation so have created an offset canvas from the front plane at the correct distance and tried to attach the canvas - however when I scale it with  exact same scale setting as the other two canvasses, it comes out much larger! How can I work around this? 

[masa.minohara]

Hi @CoastLineModels,

Thank you for posting in the forum! I think you can work around that by right-clicking on the canvas in the browser, selecting Calibrate and entering the correct value.

If that doesn't help, could you share a public link to the design with me and attach the image that you are using for Attached canvas command when you reply?