A drag count is a dimensionless unit used by aerospace engineers where 1 drag count is equal to a C d {displaystyle C_{d}} of 0.0001. A drag count is a dimensionless unit used by aerospace engineers where 1 drag count is equal to a C d {displaystyle C_{d}} of 0.0001. A drag count Δ C d {displaystyle Delta C_{mathrm {d} },} is defined as: