Note: For measuring live birds I can dull the points a bit, just ask.
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More about the mods:

Because you need to measure different things differently than 
machinists, our pointy calipers are modified in several ways. 
The slender jaws have been ground down and depth guage has 
been removed.  The depth stick can be an annoyance when 
present,  and with it gone, the moving jaw needs little force to 
get it moving smoothly. Not visibly noticeable is the light 
adjustment of the gib screws, which helps contribute to the silky 
feel. It means, however, that you must push the jaws together with 
a light, consistent touch to "zero" the instrument. When a machinists 
measure tough, strong steel cylinders OD to 0.001" they bear down 
on the jaws with significant force. When you, a biologist,  line 
up the points with some features on an animal, there is no force at 
all on the jaws. Should you ever use the flats of the jaws to measure, 
let's say a leg diameter, you will use minimal force to avoid deforming 
the relatively soft, weak structure.  So the smooth, easy movement 
isn't just nice, it is an important feature. 
   Back to the gib adjusting screws: Because they are set loosely, 
they are likely to further loosen up with use.  (Lately these screws 
have been locked from adjustment by manufacturer) These two tiny 
screws are accessed through little holes in the plastic case on the 
"top" surface where the battery hatch is located.  When the play 
gets too sloppy, "set them down" very lightly with a watch 
screwdriver.  Stop when you first feel them touch bottom, then back 
them off a tiny amount. Too tight and the sliding action will be rough, 
too loose and it will be difficult to maintain a consistent zero. It may 
take several tries at first, to get it just right. Once you have done it a 
few times, it becomes a snap.  I did not use Locktite on the gib 
adjusting screws, because of their small size even the low-strength 
type would make adjusting them difficult.   Zeroing the instrument and 
adjusting the play should be easy to do, now that you know the 
reasons for the modifications and how to make best use of them. 
  Changing the battery.  A fresh battery should last a long time .. a year 
or more, even with frequent use, it's more a matter of time even if left 
turned off. The battery you get came from the caliper manufacturer, 
it may have sat on the shelf for a year, I have no way to know. 
When it is time to change the battery, remove the little rubber hatch 
cover and gently shake it out.  If it doesn't come out easily, very 
carefully use a small watch screwdriver to gently start it moving side to 
side. As a last resort, remove the screw between the two control 
buttons, and starting at the bottom, carefully lift off the plastic cover. 
  Gick stuck to the tracks (sliding surfaces) can make the action 
sticky.  Use a slightly damp paper towel or cloth to remove water 
soluble stuff, sometimes I get in there with a Q-Tip. Then spray a 
small amount of WD40 or something similar on a paper towel to dry 
and lubricate the metal surfaces.  Don't spray anything directly on any 
part of the caliper. The front surface of the beam and capacitative 
sensor it contacts, behind the display, need to be relatively dry to work 
properly. 
  The very slender points could get bent if dropped hard, so please be 
nice to these calipers. Thanks!