I have a couple of alumnium scales that I use, and I have no problems with any of them. The nicest one is single-sided, with a small barrel that rotates to change the scale. I'd post a pciture, if I could find one online. I really recommend it.

I use a metal one. The plastic ones get chipped and crap usually builds up on there edges which eventually finds it way to your vellum. The metal ones are much easier to clean.

I have the alumnium one too, but I'll warn you. The aluminum ones tend to jump right of the drafting desk and make a startling noise as they crash on the floor at 2 in the morning.

Go for the environmentally friendly option. The embodied energy inherent in the rulers you are discussing is contributing to the immanent environmental apocalypse.

Aluminium 170 MJ/KG
Plastics 90MJ/KG

Of course my Kiln dried hardwood ruler is the best at 2.0 MJ/KG. It doesn’t handle the use of a scalpel very well but it’s the business for drafting sustainable timber framed buildings on hand made recycled paper!

Although, the arguement between aluminum and plastic is short sighted. If the aluminum is more durable, then I buy FEWER scales. Example. My cheap plastic scale already broke under normal use. Of course a plastic scale weighs less than an aluminum scale, but the production of several plastic scales will use more energy than the production of one aluminum scale.

Simple math(s) show that I could go through 85 Kiln dried hardwood rulers before losing my one flashy aluminium ruler to some light fingered office youth.

Hard Wood is so the future!

quality is my yardstick

I think everyone should ditch their scales and use those great 6" wooden rulers the vendor's give out.

you know what, just eyeball it. Looks like about 5' good enough

if the disclaimer on your title sheet says, "do not scale these drawings" then why draw them to scale?