Straight edge suitable for cutting against

[Ricardus]

I'm after a straight edge 300mm + (600 or 1000 would be better) with ruled markings that is substantial enough that I can cut against it with a stanley knife with less risk of slicing my own fingers off than a normal flat steel rule.

I'm having a real senior moment here and can't think what to Google for!

 

[cajar]

Plasterer's featheredge

 

[Norcon]

Axminster have a number of products available in their measuring/marking section.

 

[Brigadier]

My plasterer uncle just marked off his start point, put the blade to it, the dragged his finger down the edge, keeping the blade at the same distance from the edge all the way down.
Providing that the "guide" edge is straight (and you're not trying to chop too much off), this might be as accurate as you need.

 

[freddiemercurystwin]

They're just called cutting rulers eg http://www.greatart.co.uk/RUMOLDCUTTINGRULER-rulers-1.htm

Or http://www.ebay.co.uk/itm/Aluminium...Crafts_DrawingSupplies_EH&hash=item4abaefbc36

Duroedge are another make and do them with a rubber strip on the back to grip whatever you're cutting.

Cutting consistently and safely is as much about technique as the cutting edge.