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Both
are
valid,
both
produce
useful
results.
It
all
depends
on
what
you
want
to
do
with
those
results.
Spending
$4000
will
almost
certainly
give
you
more
precise,
dependable
results
than
a
$400
balance
of
equivalent
capacity.
This
does
not
mean,
however,
that
they
will
be
of
any
more
use.
Fundamentally,
the
difference
in
price
lies
in
the
type
and
degree
of
sophistication
of
the
weighing
technology
used,
and
hence
the
level
and
reliability
of
the
resolution
achievable.
The
application
will
usually
identify
the
type
of
balance
needed.
Do
you
need
to
know
absolute
weights
or
relative
values?
Do
you
need
high
levels
of
repeatability?
Do
you
need
high
levels
of
linearity?
What
other
factors
are
important
to
you
(speed,
convenience,
use
by
an
unskilled
operator,
data
collection
via
a
PC,
portability,
use
in
an
industrial
environment,
etc)?
What
most
users
believe
they
want
is
accuracy.
So
let's
start
by
exploding
a
few
myths.
What
exactly
is
accuracy?
Is
there
in
fact
any
such
thing?
Let's
assume
"accuracy"
to
be
the
balance's
ability
to
measure
a
mass
to
within
certain
acceptable
tolerance
of a
traceable
international
standard.
By
this
criterion
no
balance
is
inherently
accurate.
The
traceable
international
standard
must
itself
be
the
source
against
which
the
balance
is
calibrated.
And
there
lies
the
key.
Calibration,
using
appropriate
reference
weights*,
in a
constant
environment,
at
the
location
where
the
balance
is
to
be
used
are
the
first
steps
towards
accurate
results
and
it
is
entirely
a
matter
for
the
user
to
decide
to
which
lengths
this
process
is
taken.
The
principal
inherent
features
of a
balance
which
contribute
towards
accuracy
are
resolution,
repeatability
and
linearity.
Calibrate
with
a
500g
bag
of
sugar
and
the
balance
will
not
be
very
accurate,
but
it
may
very
well
have
excellent
resolution
and
linearity,
and
produce
repeatable
results!
Resolution
(sometimes
called
readability
or
division)
is
the
number
of
divisions
into
which
the
total
capacity
is
broken
down
for
the
purpose
of
displaying
the
weight
value.
This
is
normally
expressed
in
grams.
Thus
a
balance
may
be
described
as
1kg
(capacity)
x
0.1g
(resolution).
Repeatability
is
really
self-explanatory;
the
same
weight
placed
on a
balance
should
give
the
same
(or
near
enough
the
same)
reading
each
time,
given
stable
environmental
conditions.
It
is
the
phrase
"near
enough"
which
is
important
here.
What's
'near
enough'
for
your
purpose?
Repeatability
is
closely
tied
to
resolution
and
is
generally
quoted
as
plus
or
minus
a
given
number
of
scale
divisions.
Linearity
is
the
ability
of
the
balance
to
respond
consistently
throughout
its
capacity
range.
It
should
weigh
within
the
acceptable
tolerances
at
all
points
in
its
capacity,
not
just
at
the
calibration
points.
External
environmental
factors
affecting
performance
The
most
obvious
external
factors
affecting
performance
are
temperature
and
physical
stability,
and
both
of
these
can
be
overcome.
Most
electronic
balances
have
some
form
of
internal
temperature
compensation.
In
high
resolution
balances
it
is
often
desirable
to
re-calibrate
the
balance
whenever
the
temperature
varies
outside
predetermined
limits.
To
this
end,
analytical
balances
are
frequently
equipped
with
their
own
internal
calibration
weight
and
re-calibration
programme.
It
is
also
useful
if
the
balance
itself
alerts
the
user
to
these
temperature
changes,
which
may
otherwise
go
unnoticed.
In
any
event,
an
electronic
balance
must
be
given
adequate
time
to
stabilise
after
switching
on
before
it
performs
correctly.
For
an
analytical
balance
this
could
be
several
hours.
Physical
stability
is
improved
by
the
use
of a
draft
shield,
which
is
standard
on
balances
reading
to
0.1mg
(0.0001g)
or
less,
useful
on
0.001g
balances
but
of
doubtful
value
on a
balance
reading
to
0.1g.
Further
improvements
in
stability
can
be
introduced
by
the
use
of
an
anti-vibration
weighing
table.
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