Calipers are a lot more inaccurate on easy locks than hard ones. This doesn't matter when picking Nelemar boxes, because they are all hard.

However boxes out of Reim and OSA fall in the lock range where calipers on a capped smith don't work properly.

....

R>
Measuring carefully, it looks to be a fairly simple lock (-330 in thief-lingo difficulty ranking).

>pick strongbox with indigo lockpick
You settle into the difficult task of picking the lock.
You make a lame attempt (d100=25).
Your lockpick gets stuck in the lock! You carefully try to work it free but end up bending the tip!
Roundtime: 5 sec.
R>lm app my loc
You examine the indigo lockpick very closely. It appears to be in a neglected state. It seems to have a detrimental level of precision and is flimsy. Judging by the tip, the lockpick has been repaired about 3 times. You could probably handle a simple lock pretty easily with it.
Roundtime: 2 sec.
R>
You attach an indigo copper lockpick to a twining invar keyring.
>get cop loc
You detach a copper-edged steel lockpick from a twining invar keyring.
>pick strongbox with copper-edged lockpick
You settle into the difficult task of picking the lock.
You make a competent attempt (d100=67).
You struggle with the strongbox. As you do, you get a sense that the strongbox has a fairly plain lock (-385 thief-lingo difficulty ranking). Then...CLICK! It opens!
Roundtime: 5 sec.
R>
You attach a copper-edged steel lockpick to a twining invar keyring.
>get cal
You remove some scarab-set professional calipers from in your black stalking cloak.
>lm cal cal
You make some effort to fine-tune the professional calipers.

You can't help but think that the calipers are as finely-tuned as you are possibly going to get them. They practically glow with calibration!

Roundtime: 17 sec.

...

It shouldn't be missing by 55 when within one calibration of perfect.

Measuring again after opening the lock gave

385,395,415. The third measurement after calibration is already well outside the range it should be.

Then recalibrating and while still in perfect calibration

...

Measuring carefully, it looks to be a moderately well-crafted lock (-410 in thief-lingo difficulty ranking).
R>lm cal cal
Those calipers could not be more perfectly calibrated. You should leave them alone. You'll just mess them up.
>

...

Measurement shouldn't be missing by 25 while in perfect calibration. 15 is the most that ever happens on locks in the 800-1400 range.
The average error on measurement is about three times as large as it should be for locks around -400.
One of the adjustments to how calipers work in recent years has broken their accuracy for locks around the copper-silver range on a capped smith and with capped characters now getting this size lock dropped for them in large numbers, it matters.