Why Use a Kitchen Scale?
The first and foremost reason is of course precision. Precision is how repeatable
a measurement is. For example, if we measured a cup of all-purpose flour in a 1
cup (8 ounces) dry measuring cup, we expect the mass of the flour to be 125 grams.
Assuming that the dry measuring cup is constructed to strict standards, the cup
is accurate but not precise. Every time flour is measured, it is a bit more or a
bit less than 125 g. How tightly packed the flour is, whether it has been recently
sifted, if we scooped the flour or spooned it, all make an impact to the repeatability
or precision of using a cup as a measuring device. On the other hand, a scale is
precise (and accurate if calibrated). When a cup of flour is weighed on a scale,
it is possible to add or take away flour until the scale registers 125 g. The precision
of the scale is dependent on how easy it is to read the scale. In baking, using
a scale to measure all the ingredients will ensure that you are following the recipe
correctly (at least in terms of the proportions of ingredients). Using measuring
cups could result in having a little more flour than leavening, etc.
Types of Scales
There are three main types of scales available for use in the kitchen:balance, mechanical/spring,
Balance scales operates by performing comparisons between known masses and the object
to be weighed. (Technically, a balance determines mass not weight and is the only
type of scale that will work properly if you plan to cook on the moon. The balance
in all other disciplines is considered separate from a scale, but in cooking we
lump the two together.) The problem with the balance is that it only reports if
the object you are measuring is greater or less than the known mass. For example,
when using a balance to measure a cup of flour, 125 g of known mass is placed on
one side of the balance while flour is placed on the other side until the mass on
both sides are in balance. A beam balance has a beam with adjustable masses that
move along the beam to increase torque applied to counteract the torque on the other
end of the beam from the weight of the object being measured. (Exactly like the
physician's scale at your doctor's office.) In general, a good balance is extremely
accurate and can be extremely precise, but no matter how skilled the operator of
the balance is, I feel it's a bit slow for use in the kitchen.
Mechanical scales use a platform mounted on a heavy spring to measure weight. An
ideal spring compresses proportionally to the force applied to it. This means the
weight placed on the platform is directly related to the distance that the platform
moves down. The problem is that in actuality, springs aren't ideal. For the most
part, they do exhibit the property of linear compression, but they also may change
compression rates over time, may not return to their original length, and sometimes
even break. Also, another problem with springs is that small quantities are harder
to measure than large quantities. For example, if a scale is designed to measure
up to 5 lbs. then then measuring one ounce of something will be more difficult than
one pound. This is because the small amount of movement in the spring caused by
one ounce will be difficult to detect because the scale is designed to move evenly
throughout the whole five pounds. However, high quality mechanical scales can be
quite precise, but they also carry a hefty price tag. Cheap mechanical scales can
cost less than $10, but aren't terribly accurate or precise, but if these scales
are the only ones you can afford, purchase a set of dry measuring cups instead.
Properly used, the dry measuring cups will be more accurate and precise than the
These scales range from $25 to over $100 with the vast majority in the $50 range.
A good digital scale provides easy to read measurements with high precision. They
work based on an electrical component called a strain gauge (also known as a load
cell). The resistance of the strain gauge changes based upon the compression or
change in shape of the component. A simple computer in the digital scale is preloaded
at the factory with a table of values that allows it to calculate the weight of
a load by the change in resistance. Many scales update about once a second, but
better scales will update their readings much faster. This means, if you're pouring
sugar into a bowl, the scale will provide almost instantaneous feedback so you don't
pour too much. Most digital scales also have a tare function that allows the user
to subtract the weight of the container from the measurement.