Calibrating the Scale

I slipped out of the pantry and climbed the carved leg of the study desk before the house stirred. Resting beside an inkwell sat an open wooden drafting case holding a heavy steel vernier caliper. I pulled my punched brass transit strip from its cotton webbing and laid it flat across the tabletop. Gripping the knurled thumb wheel with both mittens, I slid the caliper jaw flush against the first switch perforation. Exactly four millimeters. Using my waxed finishing nail, I scribed fine index notches into the brass margin beside each punch hole. Unmeasured coordinates invite navigation error. Now the siding grid carries verifiable physical scale.