generally, but not necessarily, equal to the length of one of the primary divisions, 1-2-3-4 sa>'one inch, then draw nine parallel lines, dividing the rectangle into ten equal spaces. Divide tlie left-hand primary at top into ten equal parts ; these will, of course, in this case, represent tenths of an inch. Divide the bottom line similarly, and draw lines diagonally from one division at the top to the next one at the bottom. Now the lower end of each line has moved one-tenth of an inch to the. left in its passage across the rectangle, and as it is itself divided into ten equal parts, each of these parts, counting from the top, is j of -j1^, or rJ-0- of a primary nearer the left than the one immediately above it. Thus, if it is desired to measure 2-24 in., place the dividers with one leg on the primary 2, on the horizontal line 4 as at a, and stretch it out along the line until it reaches diagonal 2, as shown by the dot. Any other decimal part may be found similarly, always reading the units on the vertical lines, the tenths on the diagonal lines and the hundredths on the horizontal lines.
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