[Guest]

I thought of this when I was riding in a car looking at my watch...

You are in a car and you just entered a dark tunnel, you want to measure how much time it takes until you get out (you are not the driver), you have your watch which is on stopwatch mode but the light doesn't work, so you don't know if the watch is running or not, there are two buttons that control the stopwatch:

Start/Stop

Reset/Lap

The start stop is obvious, but the Reset/Lap button, if you press it while the watch is running the display will freeze but the watch will continue on running in the background, once you press it again it goes back to normal, if you press it while the watch is stopped it resets it to 0.

http://anzapower.webs.com/Temp/watch.swf

You can't look at the watch until you're out of the tunnel, how can you measure the time?

• You may not use an out-of-the-box solution! (e.g ask the driver, use cellphone light)
  
• It's ok if your time is ± a few seconds off
  

[Guest]

if distance = rate x time then, distance / rate = time. if it is a dark tunnel then your car lights are on, check the odometer (distance) then the speedometer (rate). you'll get your answer

[Guest]

... assuming its a watch with arrows (not electric), you put the it right next to your ear and you'll hear the ticking of the arrow moving every second. You can then just count the seconds till you see sunlight (assuming that it's day)

I've tried it and it works.

[Guest]

By the way there are some watches have that have that thingy on their arrows,so when it stays exposed to light for a long time it lights up in the dark. I have one and it does a great job sometimes.

[Guest]

What happens if the watch is paused and you press start/stop? I'll assume nothing happens.

Press the buttons in the following order:

Start/Stop

Reset/Lap

Start/Stop

Reset/Lap

When you leave the tunnel it will either be running or paused. If it is paused then you just press the lap button to show the correct time again (if i understand the OP correctly). Drawing a state transition diagram is very useful here.

[Guest]

If you don't know which button does what in the dark (I think that's the whole point) then you press both as you enter the tunnel, then press either one as soon as you get out. The stopwatch will be stopped in the right time unless you press start-reset-reset, in which case it will be running but you can determine the time with a certain accuracy, or if you press start-reset-start, where it will be showing like 0.5 seconds so you just have to press reset again to get the right time.

[Guest]

if distance = rate x time then, distance / rate = time. if it is a dark tunnel then your car lights are on, check the odometer (distance) then the speedometer (rate). you'll get your answer

That's considered an "out of the box" solution, you need to use your digital watch...

What happens if the watch is paused and you press start/stop? I'll assume nothing happens.

Press the buttons in the following order:

Start/Stop

Reset/Lap

Start/Stop

Reset/Lap

When you leave the tunnel it will either be running or paused. If it is paused then you just press the lap button to show the correct time again (if i understand the OP correctly). Drawing a state transition diagram is very useful here.

If the watch is paused abd you press the start/stop button it'll continue, if it's only paused the display (when you press the lap button while it's running) it'll also change it's state...

Check the flash file, I've programmed it to work exactly like the watch...

If you don't know which button does what in the dark (I think that's the whole point) then you press both as you enter the tunnel, then press either one as soon as you get out. The stopwatch will be stopped in the right time unless you press start-reset-reset, in which case it will be running but you can determine the time with a certain accuracy, or if you press start-reset-start, where it will be showing like 0.5 seconds so you just have to press reset again to get the right time.

You do know which button is which because the start/stop button is always on top right, reset/lap is always bottom right, mode and light buttons (not included in the riddle) are always on the left side...

At least that's the case with the dozen watches I've came across...

[Guest]

You press start/stop at the entrance to the tunnel.

Lap/reset in the tunnel.

Start/stop as you exit the tunnel, (because you cannot view the watch until you are outside the tunnel)

Then lap/reset to view you're time any time outside the tunnel. The time shown on the display will be at the time you first pressed the lap/rest button before you do this. But as you press it again, due to the fact you pressed the start/stop button, the display will now show the exact time you exited the tunnel.

I don't see why this wouldn't work, if it's not correct could you kindly explain why?

Perhaps I am misinterpreting the question.

[Guest]

You press start/stop at the entrance to the tunnel.

Lap/reset in the tunnel.

Start/stop as you exit the tunnel, (because you cannot view the watch until you are outside the tunnel)

Then lap/reset to view you're time any time outside the tunnel. The time shown on the display will be at the time you first pressed the lap/rest button before you do this. But as you press it again, due to the fact you pressed the start/stop button, the display will now show the exact time you exited the tunnel.

I don't see why this wouldn't work, if it's not correct could you kindly explain why?

Perhaps I am misinterpreting the question.

if the watch is initially running, once you press start/stop it will stop and then lap/reset will reset it.

[Guest]

The problem, as I see it, is two-fold. First, I assume you have no idea what state the watch is in (either running, running with lap time displayed, stopped, or stopped and cleared), so you must reset it to even begin.

For either of the four states mentioned above, if you quickly hit R/L, S/S, R/L, R/L you will have cleared out any prior time on the watch. If it was running or running with the lap time displayed, it will now be stopped and cleared. If it was stopped or stopped and cleared, it will begin running.

The second problem, is that the S/S button will always change the state of the watch even if the display is paused showing the lap. You want to assure that it is running, but so far I have not been able to come up with a combination of the S/S and R/L buttons that can assure that given the 4 possible starting states. So instead, I will assume that you, the watch operator, while not able to tell time, can in fact keep time, perfectly, (i.e. you are a human metronome).

Assuming you can keep perfect time, then once you clear the watch following the steps above, you need only to hit the S/S button in time to your own internal metronome. No matter what rate your internal clock is ticking at, and as long as it is at a somewhat constant rate through the tunnel, the amount of time that will have been recorded on the watch will be about half the time that it took to go through the tunnel (plus or minus a few seconds). The faster your internal metronome, the more accurate it will be.

For those of you who would balk at the thought of perfect internal rhythm, I suggest the following options to aid in your timekeeping (although, I must admit, these may qualify as out of the box).

If you're listening to a CD or mp3, you could just keep time with the music. (Radio won't work because you're in a tunnel.) Or, better yet, ask the driver to flip the windshield wipers on. Boom. Your very own metronome!

[Guest]

Solved by Louie in post #16, great job.

Though in the beginning you press R-R-S-R-R, cause there is a chance the watch is stopped but showing a lap time...

[Guest]

Solved by Louie in post #16, great job.

Though in the beginning you press R-R-S-R-R, cause there is a chance the watch is stopped but showing a lap time...

Post 16? Lol im post 12. And yes, I know its a typo.

[Guest]

Solved by Louie in post that looks like #16...

[Guest]

Solved by Louie in post #16, great job.

Though in the beginning you press R-R-S-R-R, cause there is a chance the watch is stopped but showing a lap time...

You're right. I totally missed that starting state. Great original puzzle! Really enjoyed thinking about it. Did you think to use the wipers when you originally posted?

[Guest]

Press the Reset/lap button while entering the tunnel .It will mark the time when you started the watch(It doesn't matter weather it was running in the first place or not). When you are out of the tunnel take a quick look on the watch and note the reading immidiatley and then again press the reset/lap button.You will have both the times (when you pressed the reset/lap button while entering tunnel and when again you pressed it while leaving it) and subtracting first from second would give you the total time in which you covered the distance in tunnel.

The keener is your observation, the more precise would be your time .

Edited July 19, 2010 by Harjot

[Guest]

YES! Solved by Drexlin in post 16!

[Guest]

You're right. I totally missed that starting state. Great original puzzle! Really enjoyed thinking about it. Did you think to use the wipers when you originally posted?

No, this was only about the watch, the tunnel thing is the most realistic situation I could think of, you could translate this riddle into being in a dark room by yourself with nothing around you...

Press the Reset/lap button while entering the tunnel .It will mark the time when you started the watch(It doesn't matter weather it was running in the first place or not). When you are out of the tunnel take a quick look on the watch and note the reading immidiatley and then again press the reset/lap button.You will have both the times (when you pressed the reset/lap button while entering tunnel and when again you pressed it while leaving it) and subtracting first from second would give you the total time in which you covered the distance in tunnel.

The keener is your observation, the more precise would be your time .

What if the watch is already in lap mode or is stopped?

[Guest]

No, this was only about the watch, the tunnel thing is the most realistic situation I could think of, you could translate this riddle into being in a dark room by yourself with nothing around you...

What if the watch is already in lap mode or is stopped?

Yeah, it won't work in these cases,answer must be something else.