Linear sizes and arm asymmetry of intrinsically symmetric doubles

In an intrinsically symmetric model, the distribution p_x(x) of the fractional arm difference of a sample of straight double radio sources reflects the distribution among the doubles of their orientations phi away from the line of sight. In a constant speed expansion model, the two distributions can be simply related, and the resultant distribution p_el(el) of the projected linear sizes el can be derived, to be compared with the observed distribution for the same sample. Such a calculation is illustrated using a sample of extended doubles. The model is perhaps more applicable to compact doubles. However, these are not yet numerous enough to construct usable samples.