Methods of building construction are described in the "Timberwork Manual", which, some say, was written by Yu Hao. (According to that book), buildings have three basic units of proportion, what is above the cross-beams follows the Upperwork Unit, what is above the ground floor follows the Middlework Unit, and everything below that (platforms, foundations, paving, etc.) follows the Lowerwork Unit. The length of the cross-beams will naturally govern the lengths of the uppermost cross-beams as well as the rafters, etc. Thus for a (main) cross-beam of (8 ft) length, an uppermost cross-beam of (3.5 ft) length will be needed. (The proportions are maintained) in larger and smaller halls. This (2/28) is the Upperwork Unit. Similarly, the dimensions of the foundations must match the dimensions of the columns to be used, as also those of the (side-) rafters, etc. For example, a column (11 ft) high will need a platform (4.5 ft) high. So also for all the other components, corbelled brackets, projecting rafters, other rafters, all have their fixed proportions. All these follow the Middlework Unit (2/24). Now below of ramps (and steps) there are three kinds, steep, easy-going, and intermediate. In places these gradients are based upon a unit derived from the imperial litters. Steep ramps are ramps for ascending which the leading and trailing bearers have to extend their arms fully down and up respectively (ratio 3/35). Easy-going ramps are those for which the leaders use elbow length and the trailers shoulder height (ratio 1/38); intermediate ones are negotiated by the leaders with downstretched arms and trailers at shoulder height (ratio 2/18). These are the Lowerwork Units. The book (of Yu Hao) had three chapters. But builders in recent years have become much more precise and skillful (yen shan) than formerly. Thus for some time past the old Timberwork Manual has fallen out of use. But (unfortunately) there is hardly anybody capable of writing a new one. To do that would be a masterpiece in itself!