ESDU Struct 00.07.04 gives a graph for the primary warping constant of a Z-section either with bulbs on both flanges or without bulbs. The constant is a function of the bulb area and the distance of its centroid from the centre-line of the flange, the length of the web and its effective thickness including the effect of the corner area, and the length and the thickness of the flanges, which are geometrically equal. The formula from which it is calculated is also given. ESDU Struct 00.07.00 defines the primary warping constant and ESDU 77023 provides values for lipped and unlipped channel- and Z-sections.