Grasshopper gauge
Marking a line parallel to an edge which bears a fiddle or other upstanding moulding is impossible for the usual type of marking gauge because the stock is not deep enough to lift the beam above the obstruction and the pin is too short. A ‘grasshopper’ gauge, also known as a tee gauge, provides the necessary clearance. It’s also useful for marking inside hollows.
This is always a shop-made tool, sized and shaped to suit the task in hand, typically with the fence, beam and marker all made extra long to provide the necessary reach. This example with beech fence and beam is locked by a sliding oak wedge. The reversible fence is convex on one face so that it can be used to mark from concave edges.
A metal scribing pin may be improvised from a nail sharpened to a fine point, but a long pin scribing a coarse-grained timber like oak is awkward to control and a pencil works far better. The pencil is planed to an approximate semi-circular section and locked at the required length by a complementary wedge.