Scale drawings without a computer. Set the base rail on any desk, pin a sheet to the grid board, and hide a master drawing under the blind. Trace its lines with the steel needle and the four-bar linkage redraws them at a locked 1:1.6 ratio — every copy comes out at 0.625 scale, no math and no computer. Survey pins mark found positions on the grid, and the two-position lock keeps the ratio from drifting mid-trace.

How the four-bar linkage scales down. A classic parallelogram linkage: two 7.9 in arms and two 4.9 in arms share four pivots, so the needle traces a hidden master while the scribe redraws it at a fixed 0.625x scale, a 1:1.6 ratio, on the board beneath. A two-position lock holds that ratio steady once set.

Fifty-one pieces, precisely fitted. Fifty-one separate pieces make up the kit: the base rail and its two fixed pivot bosses, two long and two short linkage arms, the needle tracer and pen-collet scribe, a two-position ratio lock, the hidden blueprint board, a gridded construction board, a hinged blind, and dozens of slender survey marker pins.

Locked ratio, hidden blueprint. A two-position ratio lock clamps the linkage at 1:1.6 so the scale cannot drift, then releases for remix tweaks. The 7.9 by 5.5 in blueprint board hides beneath a hinged blind, registering into the same notches every time, while survey pins mark positions on the grid board. Every joint keeps a fine, precise layer finish.