Nobody knew the origin of the Master Stopwatch. The earliest known owner discovered it centuries ago buried in the ground. It was described being just as rusted and ancient back then as it was now. Whoever possessed the stopwatch found that they had control over time itself. They could speed it up, slow it down, and even stop it. But more specifically, it could be used to change the age of an individual on a whim, older or younger. The watch itself was peculiar looking, with multiple buttons and dials around the outside. On the clock face, the numbers 1-100 surrounded the brim in intervals of 10. There were two hands on the clock, keeping track of a person's age and the progress between years. The most peculiar thing about the watch was that its face was split into four segments, with each segment containing different symbols that could be selected by its corresponding dial.
The top segment had two arrows, one pointing up and the other pointing down. They determined whether the effects of the watch were directed towards the user (the down arrow) or an individual in front of the user (the up arrow). The clock hands adjusted to the age of the person in question.
The left segment had three symbols. A plus symbol, a minus symbol, and a circle symbol. When selected, the plus symbol increased the age of someone, the minus symbol decreased the age of someone, and the circle symbol controlled the flow of time itself. However, although you could increase or decrease the passage of time, you couldn't reverse it.
The bottom segment had a globe symbol which determined whether the effects of the watch were noticeable to the world. If selected, only those who were aware of the watch's power would notice that anything was different. The watch would alter reality to accommodate any changes. If not selected, reality wasn't altered and anyone would have be of any changes.
The right segment had a small box that displayed the effects of time. By default, it was on "1d=1d", shorthand for "1 day = 1 day". Using the dial on the side, you could adjust it within a range of "1y(ear)=1s(econd)" to "1s=1y". The amount of time that passed in real-time was equal to the amount of time that passed for the individual being affected. For example, if set to "1mi=1m", for every minute that were to pass, the individual would age or youthen by a month, or the amount of overall time that passed in one minute would be equivalent to a month.
Finally, there were two buttons on the top of the watch. One button on the right side of the watch was what activated the effects of the watch, based on what the user had selected from the above segments. For example, down arrow, plus sign, globe on, and "1d=5y" would cause the watch to age the person holding the watch 5 years for every day that passed, with reality changing as it happened. Up arrow, minus sign, globe off, and "1mi=3y" would cause the watch to regress a person in front of the user by 3 years for every minute that passed, without reality changing as it happened. Pressing the button once started the effects while pressing it again stopped the effects.
The button on the left hand side of the watch could pause time entirely for everyone except for those people who were in contact with the watch. Those who were unpaused were able to move through paused time and could move anything (and anyone) in paused time but anything electronic wouldn't work while time was paused. The watch could still be used to age or youthen a person while in paused time, even upon someone who was paused. Pressing the button again would restart time for everyone.
Over the centuries, many have come in possession of The Master Stopwatch. Samuel Watson is even rumoured to be one of its previous owners, using it as a template for his invention of the stopwatch in a failed attempt to replicate its effects. But despite having such power over time, nobody managed to stay in possession of the watch for long. Most owners willingly gave the watch away upon realising that they couldn't handle such power and were driven mad by its effects. Eventually, its presence was lost to the world as the last owner realised that with a dangerous war looming, it would be very dangerous in the wrong hands and destroyed it. Or so it was thought. What nobody realised was he actually kept it hidden away under lock and key. Several decades later, it now sits in a beachside antique store in southern California, deliberately left unwound and overpriced to deter anyone from discovering its true powers.