<s>
Double	B-Application
mass	I-Application
analysis	I-Application
is	O
a	O
simple	O
graphical	O
method	O
to	O
evaluate	O
the	O
consistency	O
of	O
hydrological	O
data	O
.	O
</s>
<s>
It	O
is	O
a	O
commonly	O
used	O
data	B-General_Concept
analysis	I-General_Concept
approach	O
for	O
investigating	O
the	O
behaviour	O
of	O
records	O
made	O
of	O
hydrological	O
or	O
meteorological	O
data	O
at	O
a	O
number	O
of	O
locations	O
.	O
</s>
<s>
Such	O
changes	O
may	O
result	O
from	O
a	O
variety	O
of	O
things	O
including	O
changes	O
in	O
instrumentation	B-Application
,	O
changes	O
in	O
observation	O
procedures	O
,	O
or	O
changes	O
in	O
gauge	O
location	O
or	O
surrounding	O
conditions	O
.	O
</s>
<s>
Double	B-Application
mass	I-Application
analysis	I-Application
for	O
checking	O
consistency	O
of	O
a	O
hydrological	O
or	O
meteorological	O
record	O
is	O
considered	O
to	O
be	O
an	O
essential	O
tool	O
before	O
taking	O
it	O
for	O
analysis	O
purpose	O
.	O
</s>
<s>
An	O
example	O
of	O
a	O
double	B-Application
mass	I-Application
analysis	I-Application
is	O
a	O
"	O
double	O
mass	O
plot	O
"	O
,	O
or	O
"	O
double	O
mass	O
curve	O
"	O
.	O
</s>
<s>
Let	O
be	O
the	O
data	O
points	O
then	O
the	O
procedure	O
for	O
double	B-Application
mass	I-Application
analysis	I-Application
is	O
as	O
follows	O
;	O
</s>
