Is one permitted to measure for the sake of a mitzvah?
As
mentioned in the last shiur, measuring on Shabbos is an issur
d’rabanan because it is a weekday activity - 'ovda d'chol'
. However,
measuring for the sake of a mitzvah cannot be termed an 'ovda d'chol'
because it is done for the sake of a mitzvah.
Do you have examples of such measuring?
If milk fell into a
pot of chicken soup, in order to eat the soup it must be sixty times the
volume of the milk. One may estimate the volume of the soup and pasken
accordingly.
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A mikveh must hold
a certain quantity of water: if there is doubt as to whether the
mikveh contains sufficient water, one may measure the volume of water.
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Another case deals
with purity. The halacha is that impurity emanating from a dead
body can pass through a gap in the wall if the gap measures a tefach
by a tefach. It is sometimes necessary to measure this gap in order to
know whether kohanim can remain in the room adjacent to the dead body.
One may use a tape measure or ruler and measure the gap on Shabbos.
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It is imperative
that one make kiddush on a cup that holds a quarter of a lug of
wine or grape juice. If one is in doubt as to whether the cup holds
the required amount, one may measure it on Shabbos. A possible method
is to use a baby’s bottle, which has the units written on it and fill
the kiddush cup accordingly.
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One must eat a
required amount of matza and maror on Pesach night and in order to
know the correct amount, one may measure with one’s hand or with any
other measuring instrument.
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One may not walk a
distance of 2000 amos outside of the town’s perimeter. A
practical way to measure on Shabbos would be to count one’s steps,
obviously depending on whether one knows how large one’s steps are.
Accordingly one may walk that distance while keeping track of how far
one is walking from the town.
What about for the sake of a baby or for an ill
person?
The Mechaber
says
that one may measure
for the sake of the ill because it is considered measuring for a
mitzvah. The Mishna Berura explains
that healing is itself
a mitzvah and therefore measuring is a part of the mitzvah.
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One may measure
the quantity needed for medicine. This is true for powder, tablets and
liquid.
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One may measure
the amount of food and liquid required to be eaten on Yom Kippur in a
case of pikuach nefesh. Often it suffices to eat a small amount
without having to eat a full amount and one may measure this amount
when necessary.
A baby or child is
considered in halacha as having a weak system and therefore one
may measure the amount of powder needed to be placed inside the baby’s
bottle etc.
Why is “measuring time” not ossur (you look at
your watch, don’t you)?
The question is
better than the answer. It is because one is not really measuring
anything, one is merely calculating a spiritual factor. One could debate
whether taking one’s temperature is the same thing, but irrespective,
one may take one’s temperature on Shabbos when illness is an issue.
What about weighing oneself on Shabbos?
Unless there is a
medical reason, it is forbidden to weigh oneself on Shabbos. We already
mentioned that a baby or child is different and if they indeed need
weighing after a meal for health reasons it is permitted.
What about looking at a barometer on Shabbos or
at a room thermometer?
Here again we can
say that one is not really measuring anything physical, or even doing an
action of measuring, and thus one may look at them on Shabbos.
It is worthwhile
knowing that if one uses a measuring tool such as a measuring spoon and
one is not meticulous that the measure be accurate, it may be used.
One should remember this and implement it whenever
one is in doubt, whether one is permitted to measure on Shabbos or not.
