Laying tongue-and-groove plywood subfloor usually calls for at least two carpenters. As one wields a sledgehammer on the sheet to be threaded, the other is easing the tongue of this sheet into the groove of the sheets in the preceding course by shifting weight from foot to foot.
The large T-square shown here can eliminate one of these jobs. It uses a 2×6 about 4 ft. long as a crossbar, and a 2×4 handle about 5 ft. long. With the plywood panel in position, run the crossbar out on the joist tops with the handle held only 12 in. off the deck. Then pull it back with a lot of force against the grooved side of the panel while keeping the balls of your feet on the seam to be threaded.
For real efficiency, try a crew of three. One spreads the glue on the joists and flops down the plywood, the second person threads the sheets into final position with the T and tacks down the corners, and the third nails them off with a pneumatic nailer before the glue dries.
Malcolm McDaniel, Berkeley, CA