I recently purchased an antique drawing tool from 1890 known as a Cenrtolinead, or Linead from an estate sale. These tools are a tremendous aid in drawing perspective. I have known about these tools for years, and could really have used one for all my perspective work at Disney for the 10 years or so of work I have done for them.
This tool did not come with any instructions, so all I had to go on were catalogs from the early 1900's showing these for sale. They operate using 2 pins and are set to a "Y" shape and equal angles. the photos explain:
My conclusion is that this tool is far easier to use than even a ruler with the VP on your board. it is very steady and quick to use. The only drawback is that the tool must be flipped around , one blade moved and new pins inserted to draw the second VP if they are both off the board. This is a somewhat unlikely situation, but it did happen on the larger building facade sketch. the best setup would be to have 2 of these or even 3 for a 3 point perspective drawing. they would make quick work of a complicated drawing like that.
I had a talk with Jim Gurney of Dinotopia fame yesterday to see what he knew about these. He said he had heard of them, and thought of making one someday. Jim will post some of this info on his popular blog to see if we can find someone with the old instruction booklet from one of the original manufacturers. We'll see what happens!
Jim brought up an interesting question in an email to me today- what do you do if you don't want holes in your drawing board? I always used a paper clip with one end bent up or an upside down flat-headed thumbtack taped to the board or paper. this is good for balancing a ruler on for perspective points on the board or for this operation. You could also use a sheet of metal to draw on, even with a Borco cover, and Neodymium magnets about 1/2 cube size for the pins. they are so strong they won't shift...