CENT-O-GRAM
BALANCE
model 311

maker: Ohaus Corporation, Florham Park, New Jersey, U.S.A. bruine lijn

Ohaus laboratory scale

Although a letter can be weighed on it, this is not a letter scale. It is a laboratory scale, also known as an uneven arm balance. The scale is made by Ohaus Corporation, Florham Park, in New Jersey, U.S.A. This scale is listed in Ohaus catalogs as model 311. The old model 311 is a version with a round red upright, two free weights and three arms with sliding weights, and was already available in 1953. The more modern version shown here with a rectangular round upright, has four arms with sliding weights and has been for sale since about 1974. The weighing range is 311 grams, and can be read per 0.01 grams. The balance has agate bearing pans, steel knife-edge bearings, a stainless steel loose pan, and magnetic damping to quickly stop movement. The balance has a separate platform to be used for specific gravity determinations. The platform can therefore easily be adjusted to the desired height. The loose pan and the suspension bracket are numbered the same, this number is also on the back of the balance, all this to make accidental exchange more difficult.

back of the laboratory scale

The rear three arms of the balance have grooves for stepping in the windowed sliding weights. The front arm has no grooves. On the rear fourth arm, the weight can be moved from zero to 100 or 200 grams per increment of 100 grams. On the third arm, the weight can be moved from zero to 100 grams per step of 10 grams. On the second arm, the weight can be moved from zero to 10 grams per step of 1 gram. The front first arm has 100 graduations on the arm from zero to 1 gram and the sliding weight with a pointer allows reading per 0.01 gram. There are numbers on this front arm per 0.1 gram. With all weights moved maximally to the right, the supplied counterweight is added together 200 + 100 + 10 + 1 = 311 grams. The balance is intended for use in laboratories of schools and of industries, for doing chemical and other fine weighing.
Below are some more images of this special Ohaus balance.

four balance arms with sliding weights

the horizontal stripes in line indicate balance

the magnet damping by a vane between two magnets

suspension bracket	weighing with 150 grams of weights	view of the magnetic damping
the platform for the stainless steel removable pan	the stainless steel removable pan	Dutch, translated: "not for commercial purposes", a usage restriction
sticker from the Dutch supplier	Ohaus type and brand plate	on the back is the number of the loose pan and the suspension bracket
platform to be used for specific gravity determination	the number on the bottom of the suspension bracket	platform in a position for specific gravity determination
aluminum rotary knob for zero adjustment of the balance	rod on which the specific gravity platform is slid	the bottom
the balanced damper vane is 29 centimeters high	here all sliding weights are at zero on the far left	notice the grooves on the back three arms

« collection part 23 «

version: November 15, 2022

CENT-O-GRAMBALANCEmodel 311

CENT-O-GRAM
BALANCE
model 311