Attached is the best I could do, based on the rough sketch.
>The image you provided was fortunately full scale. I first opened the image file in IrfanView and checked its dimensions. Then when I inserted the Image file into TurboCAD (TurboCAD has a Tool/command specifically for that), I inserted it using the X/Y sizes ascertained from IrfanView.
>In TurboCAD, I created a rectangle to use for a "Crop Image" (another TurboCAD tool), to remove the extraneous parts of the image-- the excess grid paper.
>I then did some CAD stuff to rotate the image so that the image's grid lines were pretty much orthogonal in TurboCAD (appeared to be straight up-and-down, and side-to-side); I did that to make it easier to work with.
In TurboCAD, I "Embedded" the image; that is an option in TurboCAD's Image Manager. I made sure to hit "Apply" before exiting out of that window. Sometimes, even though we "Embed" and hit "Apply", the image still does not embed. So, if when you open my TurboCAD file, if the image is not there when you select the image (the Image Layer is currently Locked; UnLock it, to select the image), you will have to direct TurboCAD on where on your system to find it... to link it to.
Anyway... based on the rough sketch, your mandolin f-hole has an area of approximately 2.08006 inches.
« Last Edit: December 12, 2019, 10:45:25 AM by Alvin Gregorio »
Intermittent TurboCAD user since yr. 2000 (ver6.5). No formal CAD Training.
---TurboCAD: V21PP; V20.2PP; V19DL; V11.2Pro; Windows-7-Pro/64-bit; Intel-Core-i3 CPU; 2.27ghz; 4GB RAM; Intel HD Graphics (CPU based)