The adjustment of squares of various classes is effected with scraping and by reference to right-angular blocks, to lines, and to other squares which are used as standards. To try an el-square by means of a surface-table and blocks, the tool is stood on its pedestal, with the blade in contact with a side of a right-angular block that rests on the table; a square in this situation is seen in Fig. 497; and if no light can be seen between the blade and the block, the outer boundary of the square is right angular. To try the inner boundary, the tool is suspended by its pedestal on a block, as shown in Fig. 498 ; and by placing two blocks near each other, with the blade between and in contact, it is known whether the inner and outer edges of the blade are parallel to each other, and also which of the two edges may need adjustment to make both edges at right angles to the pedestal; this arrangement is shown in Fig. 499. To discover if the two broad sides of the blade are parallel to each other, straight, and also at right angles to the pedestal, the pedestal is tightly held on one block while the blade depends between two other blocks that almost touch; a square in this position is denoted by Fig. 500.

Tee-squares are adjusted with a pair of blocks that are of similar shape and dimensions; these are stood near together, and the tee-square is put with its pedestal on both blocks and its blade hanging between; while thus situated, either one of the edges of the blade may be tried, and it may be known whether both edges are parallel to each other, and also at right angles to the pedestal. A tee-square being tried in this manner is indicated by Fig. 501. It is also necessary to ascertain if the broad side of the blade is square with the pedestal; for this purpose the tool is put with the entire length of its pedestal bearing on one block, with the blade extending downwards, and the broad side at a short distance from the block; while in this condition it appears as in Fig. 502. In order to discover whether the outer side of the pedestal is at right angles with the length of the blade, the tool is stood on the table with the blade extending upwards, and one arm of the pedestal extending into a gap in a block which is put into close contact with the blade's edge; this block is shown in Fig. 503 with the square's blade in contact.

The adjustment of squares by means of lines is effected on surface tables. A table is selected having a surface about two or three feet across, on which are marked several gauge lines at right angles to each other and to the edges of the table's surface; these marks are very narrow, but deep, and are made with a scriber having a hard thin point. If all the four small sides, termed edges, of the table are at right angles, any one edge may be selected from which to exscribe lines that shall extend across the surface and be at right angles to the selected edge; but if all are not at right angles, the surface is not rectangular, and one edge, or small side, is selected for the marking. This edge is specially smoothed, planed with scraping, and also made at right angles to the table's surface, which is the face. This edge is that to which the pedestals of squares and other tools will be put when they are to be tried. When the lines are to be marked, the planed edge, which is the true edge, is used as a sort of standard, or base, from which to exscribe the gauge lines, and the principal gauge line is one which is at right angles to the true edge, and extends across the table's face somewhere about the middle. This one line is represented in Fig. 504; this Figure denotes a platten, or table, whose gauge line is marked by merely placing a large square to the true edge, and scribing a line along the edge of the blade on the table's face. Several other lines may be marked parallel to each other, and by means of the same square, if necessary. This mode of making gauge lines is effectual with a good square, but to place the line at right angles to the true edge, when a large square is not comatable, a scriber-block and straight-edge are necessary.

To mark the line or lines at right angles to each other and to the true edge, by means of a scriber-block only, it is necessary that the true edge of the platten be at right angles to one of the edges that adjoin; if the platten were thus right-angled when it was made, the marking is quickly effected by placing the platten to be marked upon another platten, or table, and scribing with a scriber-block. This is performed by placing the work edgeways upon the table, and scribing a line along at about the middle; after this, the table being marked is stood upon its end which is square to the side that was first lying on the table, and while standing the across line is marked with the same scriber-block, or with another taller one, if required. While the platten to be marked is in these two positions, several lines parallel to each other may be scribed by raising or lowering the scriber's point to various heights above the table used for scribing. The scriber-block for such purposes requires a firm, heavy bottom, in which is cut a shallow recess about a sixteenth deep, to prevent the block canting and rocking while being moved along.

If only one small side or edge of the platten is true, the scriber-block is only useful to mark a iine or lines parallel to the true edge; all other lines at right angles are marked with compasses and straight-edges. This marking is commenced by placing the true edge in contact with a table's face, and using a scriber-block to mark a line along the face to be marked, and near the middle; this line is the primary from which others are exscribed, and is denoted by No. 1 in Fig. 505. To mark a line at right angles to the primary one, and across the middle of the face, it is only necessary to make with a dotting-punch a dot at each end of the primary near the edges of the surface, and scribe a perpendicular to the primary by means of the dots as centres; this is done by using a sharp compasses, or large divider, and placing one point into one dot, and scribing an arc near the middle of the face ; one compass point is next put into the other dot, and another arc is scribed to intersect the first one in two places; these two places are points in a straight line which is at right angles to the primary, and to mark the line a straight-edge is put to both intersections, and a scriber is moved along in contact. When this line is shown, it becomes a sort of standard to which the blades of squares are put while their pedestals are in contact with the true edge of the table. The dots, arcs, and straight lines should be allowed to remain in the table's face, in order to indicate at any future time whether each arc and line is correctly scribed; and the numerical order in which the dots and lines are scribed is denoted by their numbers, the first one being the primary, and the sixth one being the primary's perpendicular. If several other lines are required to be made across the primary, they are marked by exscribing arcs from any other dots that may be made in any other places along the first line. Fig. 505 denotes the appearance of the table, but Fig. 506 indicates merely the table's face and the actual relative positions of the lines.

A square may be tried also without any standard right-angular lines whatever, and also without marking any line on a table's surface. With this object a strip of thick white paper may be stuck to a table's face with thin white lead, boiled oil, or paint, and on to the paper the blade of a square is put while its pedestal is in contact with the true edge of the table ; while thus held a line is marked on the paper with ink, or with a fine pencil point, along one edge of the blade ; the square is then put upside-down, and with the same edge of the blade touching the line just made ; while in this situation the observer looks to the blade's edge and to the ink line, and if both coincide while the square's pedestal is held tight to the table's edge, the edge of the blade is square to the pedestal. In order to try the other edge of the blade, a line is marked along it as for the other edge, and the square is put upside-down, with the same edge near the line, similar to the first marking. If the tool is far from correctness, it is necessary to mark a second ink line upon the paper, and this is done by placing the square's pedestal to the table and the blade to the line on the paper, so that one point in the blade's edge just coincides with one point in the fine, and when fixed a second line is marked along the edge of the blade, and the second line will coincide with the first only in one point, while the greatest distance between the two lines indicates twice the amount of adjustment necessary for the tool.

A bisector which consists of a tee-square having pins projecting from its pedestal is tried by placing the pins into contact with the true edge of a table and marking lines along the blade's edges, similar to the mode for trying other squares. It is also necessary to try the bisector by placing its blade across rings, and the ends of cylinders, or pieces of round iron of several sizes, and to adjust the pins with filing, so that they may be both of one shape and circular. To try the edges of the blade and pedestal, the bisector is put upon right-angular blocks, and the light is observed between, as in the method for trying other squares.

During the scraping for adjusting squares and other angular gauges, it is necessary to properly prepare the inner corners; these are the junctions of the blades with their pedestals, and require to be hollowed, which facilitates the final adjustment. Such a hollow is very small, and is made by gently driving a sharp chisel edge into the corner, and then scraping off the burs which are raised up by the light hammering. The chisel for this purpose has a small cutting end only about as wide as the small side of the blade termed the edge. When a square needs much scraping near this inner corner, the small indentation becomes lost, and in such cases the chisel is again required to make another small hollow.