【AI Deduction Manga】Episode 32: Why Was the Watch Fully Wound When It Hadn't Been Touched for Three Days? ~Power Reserve Exposes the "Never Entered the Room" Lie~

監修者 Commit Ginza
Kenji
Appraiser, we have a problem.

The hand-wound watch that "no one was supposed to have touched for three days" is inexplicably full of life.
Appraiser
I see.
So the mainspring is energetic, but the owner's testimony is tired.
Kenji
I've had times when I said I didn't eat anything during lunch break, but my stomach was full.
Appraiser
That's not a deduction, it's just an internal office sighting.
CASE FILE 32: Three Days and a Full Mainspring
  • Discovery of incident: 9:18 PM, from the humidity-controlled storage room on the 4th floor, a cloisonné dial pocket watch scheduled for exhibition disappeared.
  • In the same room, a hand-wound watch with power reserve for comparative display remained.
  • Shinji Kuzumi, the manager of the storage room, claims, "I sealed it on Monday night and haven't entered it once in three days."
  • However, the remaining hand-wound watch was operating, and its power reserve display was almost full.
  • The stated power reserve of this watch is approximately 46 hours.
  • Three people had possible access to the storage room.

① Three suspects. The calmest man was the most dangerous.

Suspect A: Yuzuru Shinonome 47 years old, Night Security Manager From 8:50 PM, confirmed surveillance footage in the B1 monitoring room. He was accompanied by multiple security guards, and shift records remain.
Suspect B: Yuna Che 31 years old, Exhibition Video Director Recording an introductory video for next day's release in the 7th floor studio. Continuous video with timecodes exists.
Suspect C: Shinji Kuzumi 39 years old, Head of Collection Management Claims, "The storage room was sealed three days ago. I haven't entered it since." He is responsible for managing the room.
Kenji
He was quite confident when he said he "hadn't entered."

He said it more strongly than I do when I report on my diet.
Appraiser
A strong statement isn't always strong evidence.
Sometimes, it's just a loud voice.

② Kuzumi's Testimony - "I haven't entered the storage room for three days since Monday."

Kuzumi's Testimony:
"I locked the storage room and applied the seal after 7 PM on Monday. I haven't entered it once until I opened it on Thursday night. I don't know why the cloisonné pocket watch is gone, but at least I haven't entered the room, so I couldn't have touched it."
Kenji
He emphasized both "not touched" and "not entered" quite a bit.
Appraiser
Then, the mainspring of the remaining watch will take the stand.

Hand-wound watches don't say much, but they are surprisingly honest.

③ Power Reserve is the "Mainspring Fuel Gauge".

Appraiser
The power reserve indicator shows how much power the mainspring of a mechanical watch has left.

Especially for hand-wound watches, the reserve generally decreases unless it is wound.
Kenji
So, it's like a smartphone battery charge, right?

Except, instead of plugging it in, a person winds it manually.
Appraiser
Exactly.
This watch is hand-wound with a stated power reserve of approximately 46 hours. If left untouched for three days, or about 72 hours, it should normally stop or have significantly less reserve.
Left untouched for three days (approx. 72 hours) > stated approx. 46 hours

If no additional winding is performed manually, it is unnatural for it to remain near full.
However, the actual rate of depletion varies depending on the movement, positional error, and condition, so we cannot make an immediate judgment based solely on the display.
Clue 1: What the power reserve indicator tells us
Display Status Meaning Importance in this deduction
Near full High probability that the mainspring was recently wound properly Tends to contradict "not touched for three days"
Mid-range Operating with a moderate amount of power left Difficult to determine when it was wound based on this alone
Near zero / Stopped Power depleted or nearly depleted Consistent with a claim of being left untouched for a long time

④ On Monday when it was stored, the reserve was "about 30%".

Pre-storage confirmation record from Monday at 7:11 PM
Confirmer Appraiser, Shinji Kuzumi, and 3 record staff members
Subject Hand-wound watch with power reserve for comparative display
Condition at that time Watch operating, power reserve display at approx. 30%
Note Only time check performed during photo shoot check. No additional winding recorded.
Evidence Photo before storage, time-stamped video, confirmation sheet
Kenji
30% on Monday.

If it's nearly full on Thursday, that's beyond natural recovery; it's sheer "guts."
Appraiser
The mainspring doesn't respond to willpower.
If it increased, someone wound it.

⑤ However, when opened on Thursday, the watch was "running and almost full".

Video of opening on Thursday, 9:18 PM
Watch Condition Second hand operating, time display advancing
Power Reserve Display Approx. 90% to almost full
Storage Room Condition Only the cloisonné dial pocket watch was missing. The watch for comparative display remained on the desk.
Unnatural Point If untouched and uninhabited for three days, there's no explanation for the increase in power reserve.
Decisive Clue for the Reader:
The power reserve of the hand-wound watch was about 30% on Monday, but nearly full on Thursday. For this change to occur in a watch with a stated power reserve of about 46 hours, it is natural to assume that someone wound it at some point.
Appraiser
If Kuzumi-san says he "hasn't touched the room or the watch for three days," this display cannot be explained.

The power reserve is a silent contradiction.
Kenji
It's like the "I didn't eat the pudding from the fridge, but the spoon is washed" problem of the watch world.

⑥ However, the power reserve doesn't tell us the "name of the culprit".

Kenji
So, is the person who wound it confirmed to be the culprit?
Appraiser
I can't say that much.

What the power reserve indicates is "the possibility that someone recently touched it."
Who, why, and when they touched it needs to be determined with other evidence.
Clue 2: What the power reserve display can and cannot tell us
What it can tell us What it cannot tell us
High probability of being recently wound Who wound it
Can contradict claims of long-term non-contact Exactly when it was wound
Indicates an anomaly in the machine's reserve display Whether the act was immediately for the purpose of theft

⑦ The electronic log was clear. However, an "old maintenance key" was in use.

Traces of entry found in additional investigation
Electronic Entry Log No records from Tuesday to Thursday
Maintenance Key Borrowing Log Tuesday 8:06 PM, Kuzumi borrowed an old mechanical key, citing "humidity sensor inspection"
Seal Subtle steps and air bubbles suggesting it was peeled off and re-attached once
Traces in the Room Fibers matching Kuzumi's white gloves on the edge of the desk, scuff marks from a tool bag near the humidifier
Kenji
We thought we were safe because there were no electronic logs, but it was an analog intrusion.

It's a high-tech facility, but the entrance is an old-fashioned loophole.
Appraiser
Sometimes, old keys can unlock the loopholes of new systems.
In both deduction and operation, such "exception points" are dangerous.

⑧ Furthermore, the missing pocket watch was found not "behind the humidifier," but in Kuzumi's tool bag.

Discovery of Physical Evidence
  • The missing cloisonné dial pocket watch was found at the bottom of Kuzumi's tool bag.
  • The pocket watch was wrapped in a protective cloth, and fibers of the same type used for shelves in the storage room were attached.
  • Inside the bag were spare sealing stickers, thin tweezers, and a work memo for "humidifier inspection."
  • Kuzumi initially explained it as "for maintenance inspection," but could not explain the presence of the pocket watch.
Kenji
If stolen goods are found in a tool bag, "it just happened to be there" is no longer a viable excuse.
Appraiser
Moreover, if Kuzumi-san hadn't wound the watch, his lie of "not entering for three days" wouldn't have collapsed so quickly.

His diligence, ironically, became his undoing.

⑨ Crime Recreation - Kuzumi opened and closed the "sealed room" himself.

Kuzumi's Actual Movements
  1. On Monday night, immediately after sealing the storage room, he was looking for an opportunity to take out the cloisonné pocket watch intended for exhibition.
  2. On Tuesday night, he borrowed an old maintenance key, citing a humidity sensor inspection.
  3. He peeled off the seal, entered the storage room, and hid the cloisonné pocket watch in his tool bag.
  4. At that time, seeing the hand-wound watch with power reserve on the desk about to stop, he unconsciously wound it due to his habit as an exhibition staff member.
  5. He reattached the seal, creating the impression of "a room no one had entered for three days."
  6. When the room was opened on Thursday, the almost full power reserve display quietly revealed his recent entry.
Appraiser
Kuzumi-san didn't just break in to steal.
His professional habit of "keeping exhibits in perfect condition" led him to wind the remaining watch as well.
Kenji
He tidied up the scene too much, essentially gilding his own footprints.

⑩ The Culprit: Shinji Kuzumi, Head of Collection Management

What was full was not the watch, but the "unraveling of a lie."

Appraiser: "Kuzumi-san. You didn't stay out for three days. You entered the storage room on Tuesday night and took out the pocket watch."

Appraiser
On Monday, when it was stored, this hand-wound watch's power reserve was about 30%.

However, when it was opened on Thursday, it was almost full and operating.
It is unnatural for a hand-wound watch with a stated power reserve of about 46 hours to do that without additional winding.

Furthermore, you borrowed an old maintenance key on Tuesday and reattached the seal.
The missing pocket watch was found in your tool bag.

You entered the room, took it out, and even wound the exhibit watch.
Kuzumi's Confession:
"The exhibition kept being postponed, its appraisal didn't go up, and my personal finances were tight. I intended to temporarily take out the cloisonné pocket watch, show it to a buyer, and then return it. When I entered the storage room, the watch on the desk seemed about to stop... and I wound it out of habit. I never thought that would destroy my alibi."
Kenji
Getting caught because you were too meticulous at work—in a way, it's a professional tragedy.
Appraiser
The moment he took care of the watch, he could no longer take care of his lie.
It's ironic, but machines remember such things.

⑪ After the incident, Kenji begins to manage his "satiety" with a power reserve display.

Kenji
Appraiser, my stomach today is probably at 95% power reserve.

But I can still wind up for ramen.
Appraiser
There's no indicator on your stomach.
And stop with the over-winding.
Kenji
But I'm near zero every evening.
Appraiser
(That's just a growing boy, or a sales department that assumes overtime...)

Conclusion: What the power reserve revealed was the fact that "someone had recently touched it".

Appraiser
The power reserve indicator is vital information showing the remaining mainspring power of a mechanical watch.

In this case, a hand-wound watch that was at approximately 30% on Monday was operating at almost full power on Thursday.
This anomaly created a flaw in Kuzumi-san's explanation of "not touching it for three days" and "not entering the storage room."

However, the power reserve display alone did not determine the culprit or the exact time.
The lending of the old key, the reattachment of the seal, the traces inside the room, and the stolen item in the tool bag.
Only by combining these could the crime be proven.

The power reserve doesn't serve as an alibi. However, it can be a quiet and sharp clue to question "whether it was truly left untouched."
Learning about Power Reserve Displays from the Case
  • Power reserve is an estimate of mainspring remaining power: Especially for hand-wound watches, it generally decreases if not wound.
  • Stated duration is an important comparison factor: It varies greatly depending on the model, such as 46 hours, 72 hours, or 8-day power reserve.
  • Do not make a definitive judgment based solely on the display: It changes with positional error, condition, and winding amount, so it has limitations as sole evidence.
  • If "the reserve has increased," recent intervention can be suspected: This may contradict claims of long-term non-contact.
  • Final judgment is made in conjunction with other evidence: It requires verification with entry/exit records, footage, physical evidence, and testimonies.
Method Main Characteristics Relevance to This Case
Manual-winding watch Wound by human operation. If left untouched, the power reserve decreases. Provides a good hint for considering "when it was last touched."
Automatic-winding watch Winds with wear. A watch winder may also be used. Interpretation of power reserve changes is somewhat complex.
Long power reserve watch Some models can run for several days to over a week. Do not jump to conclusions without checking the stated power reserve time.
*The accuracy and depletion rate of power reserve displays vary depending on the movement's design, maintenance status, winding amount, and position. In this work, the deduction is based on the premise of a manual-winding watch with a stated power reserve of approximately 46 hours, with approximately 30% remaining on Monday. The culprit or entry time cannot be determined solely from the power reserve display. The incident, characters, facilities, and watches are all fictional.
Key Deductions for This Case
  • The manual-winding watch, which had about 30% power remaining on Monday, was almost fully wound by Thursday.
  • Given a stated power reserve of approximately 46 hours, this was inconsistent with "no contact for three days."
  • However, this was not determined solely by the display but combined with the old-style key lending, sealed tape, fiber traces, and stolen goods in the tool bag.
  • The watch's display did not identify the culprit, but exposed a "contradiction in the explanation."
NEXT CASE
Episode 33: How could the moon, not set since yesterday, be perfectly aligned tonight?
〜The Moonphase Reveals the Lie of "It Was Left Untouched"〜
  • The suspect claims, "I haven't touched that watch."
  • However, the moonphase display is oddly perfect for tonight's lunar phase.
  • The moon is in the sky, but the lies are waning on the dial.
Next time, Kenji will even start explaining his mood by the moonphase!
*The moonphase alone is not conclusive evidence. The next deduction will also combine multiple pieces of evidence.

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