[Illustration: Fig. 579.--Diagram of the Queen dial decade portable testing set. Its dimensions are 9-1/2" long, 7" wide and 7" deep, and weighs 11-1/2 pounds. The resistances are arranged upon the dial decade plan, being placed in circuit by means of a rotating switch contact. The switches are so constructed that they may be turned in either direction, thereby permitting them to be turned quickly from the highest resistance in any dial to the lowest resistance in the same dial. This arrangement avoids the necessity of turning back through all the remaining resistances in any particular group of coils and is of value in locating swinging crosses or conditions of momentary balances. The connections for the various tests are made by the manipulation of one small knife switch (W.B.--M.L.) and the switch BA.; these are plainly lettered, thus avoiding the necessity of referring to a diagram of connections. In construction, the dial switches are made up of eight laminations of No. 28 B. & S. phosphor bronze, and the form is such as to prevent wearing grooves on the top of the contact studs. In this instrument the electrical circuits are soldered throughout excepting the switch contact whose resistance is negligible. The resistances are wound with manganin. The battery comprises six cells sub-divided which are easily replaceable. The galvanometer is the same as in the Queen acme set, but has the addition of an Ayrton shunt, which is useful in making insulation measurements. The necessary keys, binding posts, and switches are provided so as to facilitate the use of the instrument for the various measurements that can be made with it.] Table Showing the Best Values of Bridge Arms for Measuring any Desired Resistance | | Position of| | Best Values of| Commutator| | | Plugs as| Value of Resistance being measured | | | shown in| | A = | B = | fig. 582| --------------------------------------+-------+-------+------------| Below 1.5 ohms | 1| 1,000| PQ| Between 1.5 and 11 ohms | 1| 100| PQ| " 11 and 78 ohms | 10| 100| PQ| " 78 and 1,100 ohms | 100| 1,000| PQ| " 1,100 and 6,100 ohms | 100| 100| PQ or ST| " 6,100 and 110,000 ohms | 1,000| 100| ST| " 110,000 and 1,110,000 ohms | 1,000| 10| ST| " 1,110,000 and 11,110,000 ohms | 1,000| 1| ST| Ques. In testing with the Queen Acme set how should the plugs be placed in the commutator? Ans. Always make the arm A the smaller except when the two arms are of equal value.