Grade Line. A properly drawn set of plans will show both the present lay of the ground upon which the building is to be erected and the new grade line which is to be established after the building is completed. The most convenient method of determining old grade lines and of establishing new ones is by means of the transit, Fig. 1, or the Y- level, Figs. 3 and 5, with the rod, Fig. 2. Both instruments operate upon the same principle in grade work. The telescope is set level and sights taken thru it to the target upon the rod. The reading of the target's position upon the rod compared with the height of the telescope above the base, usually the street walk, determines the difference in grade of that particular placing of the target.
Fig. 5. Taking Sights with Y- Lcvcl.
To locate levels for the masonry, (1) set the instrument at some convenient place and level the dial. (2) Having determined the height of the instrument above some predetermined base, such as the street walk, swing the telescope about and, making allowance for the difference in level as shown by the drawings, place successively stakes at each corner of the building with the required level marked thereon. As a rule, the mason has his own Y- level and uses it freely as the wall is constructed, especially where levels are to be maintained as the layers of material are placed.
Fig. 6. Leveling with Straight-edge.
In a similar manner the earth grade about the building may be located, stakes being driven into the ground at frequent intervals and the amount of " fill " or reduction indicated thereon. Grade levels are established usually only after the builders are thru, except that the mason will have the grade indicated for him where the wall above the grade is to be differently finished from that below.
Where no surveyor's level is at hand, the mason or carpenter will secure the levels by means of a straight-edge of some 14 feet in length. A common level is placed upon this plank as shown in Fig. 6. By successive levels with stakes driven to indicate the successive levelings, a grade may be carried quite a distance without very great variations.