Letting
π
:
X
→
Y
\pi :X\rightarrow Y
be a one-block factor map and
Φ
\Phi
be an almost-additive potential function on
X
,
X,
we prove that if
π
\pi
has diamond, then the pressure
P
(
X
,
Φ
)
P(X,\Phi )
is strictly larger than
P
(
Y
,
π
Φ
)
P(Y,\pi \Phi )
. Furthermore, if we define the ratio
ρ
(
Φ
)
=
P
(
X
,
Φ
)
/
P
(
Y
,
π
Φ
)
\rho (\Phi )=P(X,\Phi )/P(Y,\pi \Phi )
, then
ρ
(
Φ
)
>
1
\rho (\Phi )>1
and it can be proved that there exists a family of pairs
{
(
π
i
,
X
i
)
}
i
=
1
k
\left \{ (\pi _{i},X_{i})\right \} _{i=1}^{k}
such that
π
i
:
X
i
→
Y
\pi _{i}:X_{i} \rightarrow Y
is a factor map between
X
i
X_{i}
and
Y
Y
,
X
i
⊆
X
X_{i}\subseteq X
is a subshift of finite type such that
ρ
(
π
i
,
Φ
|
X
i
)
\rho (\pi _{i},\Phi |_{X_{i}})
(the ratio of the pressure function for
P
(
X
i
,
Φ
|
X
i
)
P(X_{i},\Phi |_{X_{i}})
and
P
(
Y
,
π
Φ
)
P(Y,\pi \Phi )
) is dense in
[
1
,
ρ
(
Φ
)
]
[1,\rho (\Phi )]
. This extends the result of Quas and Trow for the entropy case.