We paired this Tissot chronograph with our Smooth Calfskin strap in taupe for a classic chronograph look that is suitable for any occasion.

It means that the input to flip flop must be stable for some amount of time before (setup time) and after (hold time) the clock edge. If the input is changing when there is a clock edge, it cannot sample it reliably as logic 1 or logic 0, and depending on what kind of paths the clock and data propagates inside the flip flop, there might be a short glitch on the output, or the inverting and non-inverting outputs could output same data while they should output complementary data.

As you may know, Tissot and Omega merged in 1930. After the economic crisis of 1929, Tissot was in trouble and, thus, found a reprieve in partnering with Omega. This relationship explains why this Tissot chronograph uses the famed caliber 321 chronograph movement often seen in Omega chronographs, including Pre-Moon Speedmasters from the 1950s and 60s. The 321 was actually developed all the way back in the 1940s, the period that this Tissot was produced, as a product of Lemania, another partner of Omega.

If a clock pulse is given to the input of the flip flop at the same time when the output of the flip flop is changing, it may cause instability to the circuit.

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I am reading this book, "Digital Electronics & Computer Design - By M.M. Mano". While I was reading the Sequential logic and flip-flops, I found this:

The dial has developed a patina with consistent light spotting throughout and a few tiny scratches and marks. There is a shadow on the dial from the hands coming from the center towards the 11 o'clock marker, collectors refer to this as radium burn. The lume on the dial has developed patina and has aged to a dark color. The lume on the hands has also developed patina and is  a bit greener than that of the dial. The lume in the hands has possibly been redone, they glow the same under UV and fall off at the same rate as the lume on the dial. The hands have developed patina.

The crown is correctly unsigned. The dial, case, and movement are signed by Tissot. This watch was photographed on a 175mm/6.9inch wrist.

The feedback path between combinational circuit and memory elements(flip-flops) in a sequential circuit can produce instability if the outputs of memory elements are changing while the outputs of the combinational that go to flip-flop inputs are being sampled by the clock pulse.

The output of the flip flop will update to new state only after some propagation time, so if there is a feedback from flip flop output back to input, it means that the clock edges must not happen too rapidly, so that the output has been stable for enough time to satisfy the input setup time, and the flip flop output must not change too early to satisfy the input hold time as well.

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We don't see all too many Tissots from this period. Actually, examples from this Omega/Tissot era of the brand's history are quite sought after by collectors today for not only their relative rarity but for their quality. The example we have here is in great condition and features, beyond that caliber 321 movement, a pulsometer scaled dial. This is that little detail really throwing this watch over the edge of cool and interesting. The dial also is two-tone with a silver track around the numbers. On the movement, we see a "HON" mark indicating that the watch was imported into the US for the original sale.

This Tissot is in overall great and honest condition. The case is strong with light scratches and nice edges to the subtly twisted and faceted lugs. The case has some light nicks on the edges. The bezel edges have remained sharp. The engravings on the caseback are all strong and clearly visible.

I tried to get my head around this but didn't come up with any idea that gets me peace. I'm confused especially with this "the outputs of memory elements are changing or when the output of the flip flop is changing. What does it mean? Because the output of a flip-flop will only change if there's a change applied on input signal. It will not change by itself.