<s>
In	O
systems	O
engineering	O
,	O
the	O
system	B-Application
usability	I-Application
scale	I-Application
(	O
SUS	O
)	O
is	O
a	O
simple	O
,	O
ten-item	O
attitude	O
Likert	O
scale	O
giving	O
a	O
global	O
view	O
of	O
subjective	O
assessments	O
of	O
usability	B-General_Concept
.	O
</s>
<s>
It	O
was	O
developed	O
by	O
John	O
Brooke	O
at	O
Digital	O
Equipment	O
Corporation	O
in	O
the	O
UK	O
in	O
1986	O
as	O
a	O
tool	O
to	O
be	O
used	O
in	O
usability	B-General_Concept
engineering	O
of	O
electronic	O
office	O
systems	O
.	O
</s>
<s>
The	O
usability	B-General_Concept
of	O
a	O
system	O
,	O
as	O
defined	O
by	O
the	O
ISO	O
standard	O
ISO	O
9241	O
Part	O
11	O
,	O
can	O
be	O
measured	O
only	O
by	O
taking	O
into	O
account	O
the	O
context	O
of	O
use	O
of	O
the	O
system	O
—	O
i.e.	O
,	O
who	O
is	O
using	O
the	O
system	O
,	O
what	O
they	O
are	O
using	O
it	O
for	O
,	O
and	O
the	O
environment	O
in	O
which	O
they	O
are	O
using	O
it	O
.	O
</s>
<s>
Furthermore	O
,	O
measurements	O
of	O
usability	B-General_Concept
have	O
several	O
different	O
aspects	O
:	O
</s>
<s>
Thus	O
,	O
it	O
can	O
be	O
difficult	O
,	O
if	O
not	O
impossible	O
,	O
to	O
answer	O
the	O
question	O
"	O
is	O
system	O
A	O
more	O
usable	B-General_Concept
than	O
system	O
B	O
"	O
,	O
because	O
the	O
measures	O
of	O
effectiveness	O
and	O
efficiency	O
may	O
be	O
very	O
different	O
.	O
</s>
<s>
However	O
,	O
it	O
can	O
be	O
argued	O
that	O
given	O
a	O
sufficiently	O
high-level	O
definition	O
of	O
subjective	O
assessments	O
of	O
usability	B-General_Concept
,	O
comparisons	O
can	O
be	O
made	O
between	O
systems	O
.	O
</s>
<s>
SUS	O
has	O
generally	O
been	O
seen	O
as	O
providing	O
this	O
type	O
of	O
high-level	O
subjective	O
view	O
of	O
usability	B-General_Concept
and	O
is	O
thus	O
often	O
used	O
in	O
carrying	O
out	O
comparisons	O
of	O
usability	B-General_Concept
between	O
systems	O
.	O
</s>
<s>
Recently	O
,	O
Lewis	O
and	O
Sauro	O
suggested	O
a	O
two-factor	O
orthogonal	O
structure	O
,	O
which	O
practitioners	O
may	O
use	O
to	O
score	O
the	O
SUS	O
on	O
independent	O
Usability	B-General_Concept
and	O
Learnability	O
dimensions	O
.	O
</s>
<s>
At	O
the	O
same	O
time	O
,	O
Borsci	O
,	O
Federici	O
and	O
Lauriola	O
by	O
an	O
independent	O
analysis	O
confirm	O
the	O
two	O
factors	O
structure	O
of	O
SUS	O
,	O
also	O
showing	O
that	O
those	O
factors	O
(	O
Usability	B-General_Concept
and	O
Learnability	O
)	O
are	O
correlated	O
.	O
</s>
<s>
Based	O
on	O
a	O
review	O
of	O
hundreds	O
of	O
usability	B-General_Concept
studies	O
,	O
Sauro	O
and	O
Lewis	O
proposed	O
a	O
curved	O
grading	O
scale	O
for	O
mean	O
SUS	O
scores	O
.	O
</s>
