Adjustable Allbrit planimeter calibrated for imperial units. Assembled to use with the magnifier which can be rotated. There is a checking bar. One revolution = 10 sq inches. Accessory box covered in leatherette with blue velvet padding.Inside the box (insert): 'SCALE / VERNIER POSITION ON TRACER BAR / AREA OF ONE REVOLUTION OF THE MEASURING WHEEL SCALE / ACTUAL / CONSTANT / SCALEallbrit planimeter, mathematical instruments