Instructions from 1950’s Semco Crochet booklet
BLOCKS (bl): Are formed by working trebles in adjoining stitches for the required number.
Where blocks are consecutive there are four trebles in the first block and three trebles in each following block.
Therefore, to find the number of trebles in a row of blocks, multiply the number of blocks by three and add one, in two blocks there are seven trebles, in three blocks, ten trebles, etc.
SPACES (sp): To form a space, make one treble, then chain two, skip two stitches of previous row and make another treble. This should result in a perfect square, but perfection requires persistent practice as well as the correct sizes of needle and thread.
For a space at the beginning of a row, chain five, which allows three for the treble on the edge, and two for the usual chain, two at top of space.
Digital version of this pattern is © Sarah Bradberry