Pentax P5 - Exposure-Memory Lock

The exposure-memory lock enables you to take an exposure reading
in the Programmed AE or Aperture-Priority AE mode, lock-in that
reading, move your position, and then take the picture with the
programmed reading. This is particularly useful in high-contrast
conditions, such as when your subject is back-lit or has a dark
background.
1. If you are taking a portrait, you can move in close to your
subject and take a close-up reading of the face. To hold that
reading, depress the memory-lock button; this will hold the
reading for about ten seconds, simultaneously making the
shutter speed (LED) you are using flicker in the viewfinder at
a faster speed.
2. As long as you keep depressing the shutter button halfway while
the memory lock is in use, the memory lock will be maintained
or, in other words, the exposure will remain the same.
• When you wish to interrupt the memory lock, just turn the main
switch off.