Pentax K-7 Operating Manual page 118

EV Compensation for M and X modes
For example, if the EV compensation value is set to +1.5 for M
(Hyper-manual) and X (Flash X-sync speed) modes, an
underexposure of 1.5 EV is displayed on the EV bar. If you set the
exposure value so that the | is displayed at the center of the EV bar,
the image will be captured with the compensated value.
Set the exposure steps in [1. EV Steps] in the
[C Custom Setting 1] menu (p.85) to
increments of 1/3 EV or 1/2 EV.
Step interval Exposure setting Value
1/3 EV +0.3, +0.7, +1.0, +1.3, +1.7, +2.0, +2.3, +2.7, +3.0, +3.3, +3.7,
+4.0, +4.3, +4.7, +5.0
1/2 EV +0.5, +1.0, +1.5, +2.0, +2.5, +3.0, +3.5, +4.0, +4.5, +5.0
AE lock is a function that locks the exposure prior to taking the picture. Use
this when the subject is too small or backlit and a proper exposure setting
cannot be obtained.