I'm having a bit of a senior moment I think. I wish to scale up some drawings from 4 to 7 mm scale but can't for the life of me remembber the ratio. Help please. Thank you.

Multiply by 1.75?

That'll do it. Muchas Gracias sir.

I use a simple method. Get a large (A3 at least) sheet of Graph paper (1mm squares). Mark the vertical side every 4mm from the bottom and the horizontal side every 7mm. Draw a diagonal lie to represent 1ft, 2ft etc. Then by using a pair of dividers transfer the 4mm size details onto the upright scale, draw to thin line to where it meets the diagonal line and then drop that line down to the 7mm scale line. That is the new length in 7mm scale. It's easier to do than it is to describe.