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Thread: Smiths PRS-68

  1. #1

    Smiths PRS-68

    Where can I find information about the PRS-68 diver?

  2. #2
    Master Lampoc's Avatar
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  4. #4
    Grand Master abraxas's Avatar
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    I read that a couple of weeks back. What a magnificent review!!!

  5. #5
    Grand Master Seamaster73's Avatar
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    Said it before and I'll say it again, one of the best things about a new watch from Eddie is getting a new review from Ewan.

  6. #6
    Craftsman James_'s Avatar
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    This just completely changed my view on the Miyota 9015.

    "One aspect of the calibre’s simplicity is the unidirectional winding of the rotor – in layman’s terms, the rotor winds the mainspring when it rotates in one direction; if it rotates in the other then it does not – it freewheels. I always had mixed feelings about this arrangement without really doing any research. Being so impressed with the PRS-68 in all other aspects thus far, I thought I would see if there might be any benefit (apart from mechanical simplicity) of the unidirectional winding system.

    I am lazy, without doubt. Or perhaps to be fair, my lifestyle is relatively sedentary. If I am wearing an automatic watch the winding of such needs to be efficient; and to my delight, it appears that with a non complicated automatic movement (e.g. no chronograph) then unidirectional winding is the order of the day. It has been proven to be more efficient than bidirectional winding in many conditions – including those of slouches like me.

    The technical aspects of this (which I shan’t explore in any depth) concern inertia and dead angles – basically, the less mechanical resistance that the winding mechanism has to overcome in order to wind the mainspring then the more quickly the mainspring will become wound. A bidirectional system uses a relatively high proportion of the angle of swing of the rotor when the rotor changes its direction of rotation just to get the reverser mechanism ‘sorted out’ before transmitting energy to the mainspring. This is particularly critical when small movements of the wrist translate into gentle back and forth rocking of the rotor. A good proportion of that gentle rocking is not actually doing anything apart from setting the reverser mechanism (whatever type it might be) ready for further rotation of the rotor which might not actually take place.

    A unidirectional winding system on the other hand, has no reverser mechanism. Whilst the rotor is moving in the non winding direction it is doing nothing for the mainspring (and we can hear it freewheeling); but the vast majority of energy from the slightest movement in the winding direction is transmitted efficiently – the dead angle is less and the mainspring is wound more.

    For those who are very active this is perhaps rather academic. I have always wanted to feel as confident in something that is purported to be doing ‘half a job’ as one which goes the whole way and Jaeger LeCoultre’s findings have allayed any fears I may have had; as reported in Watchtime Magazine:

    “We tested Caliber 899 in two ways, in the standard version with bidirectional winding and in an altered form with unidirectional winding. Unidirectional winding was significantly slower on the Cyclotest machines. But we also asked different people to wear these watches on their wrists. We gave them wristwatches with slack mainsprings and asked them to wear them from 8 a.m. to 4 p.m. On average, watches with unidirectional winding were twice as strongly wound as watches with bidirectional winding.”

    I decided to conduct my own experiment on the basis of the above. With the PRS-68 absolutely stopped, no power at all, I gently twisted it and tilted it back and forth for precisely three minutes. I didn’t put it on my wrist, just held it and moved it. It took almost all of those three minutes to get up and running but once the seconds hand was scurrying its way along, I set the watch back in the box and waited. From those three minutes of movement the watch ran for no less than 6hr 25min. Thus, it appeared that three minutes of movement gave me about one seventh of total power reserve! Very impressive. Next, I did exactly the same with a brand new Seiko 4R36 (bidirectional winding) equipped watch, moving the watch in very much the same way as the Smiths for the same amount of time – the Seiko ran for 3hr 55min. Whilst my little experiment wasn’t particularly scientific, it seemed to back up JLC’s findings and it has to be said, gives me great confidence in the Miyota 9015. It is more efficient than an equivalent mainstream Seiko movement – for me anyway. For those more active then the chances are that both systems are just about equal."

  7. #7
    Administrator swanbourne's Avatar
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    Whole chunks of my life come under the heading "it seemed like a good idea at the time".

  8. #8
    Grand Master abraxas's Avatar
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    This just completely changed my view on the Miyota 9015.
    Unidirectional is actually better than bidirectional... because there are less parts to go wrong or wear out. Performance wise, it makes no difference.

  9. #9
    Master
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    Quote Originally Posted by swanbourne View Post

    One on eBay now. With three days still to go the bidding has reached £470.
    Last edited by seabiscuit; 12th February 2019 at 08:24.

  10. #10
    Craftsman James_'s Avatar
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    Quote Originally Posted by abraxas View Post
    Unidirectional is actually better than bidirectional... because there are less parts to go wrong or wear out. Performance wise, it makes no difference.
    I know that now because I did read the part I quoted and posted. Although I doubt if "less parts to go wrong" comes into it.

    The wobble is still annoying though and I would still choose a 6R15 over a 9015 every time. I probably won't hesitate to buy a 9015 powered watch now though.

  11. #11

    Smiths

    I missed the one on mywatchmart, keeping a sharp eye on the one on Ebay.

  12. #12

    Smiths

    A lot of good information since I'm not familiar with the 9015 movement.






    Quote Originally Posted by James_ View Post
    This just completely changed my view on the Miyota 9015.

    "One aspect of the calibre’s simplicity is the unidirectional winding of the rotor – in layman’s terms, the rotor winds the mainspring when it rotates in one direction; if it rotates in the other then it does not – it freewheels. I always had mixed feelings about this arrangement without really doing any research. Being so impressed with the PRS-68 in all other aspects thus far, I thought I would see if there might be any benefit (apart from mechanical simplicity) of the unidirectional winding system.

    I am lazy, without doubt. Or perhaps to be fair, my lifestyle is relatively sedentary. If I am wearing an automatic watch the winding of such needs to be efficient; and to my delight, it appears that with a non complicated automatic movement (e.g. no chronograph) then unidirectional winding is the order of the day. It has been proven to be more efficient than bidirectional winding in many conditions – including those of slouches like me.

    The technical aspects of this (which I shan’t explore in any depth) concern inertia and dead angles – basically, the less mechanical resistance that the winding mechanism has to overcome in order to wind the mainspring then the more quickly the mainspring will become wound. A bidirectional system uses a relatively high proportion of the angle of swing of the rotor when the rotor changes its direction of rotation just to get the reverser mechanism ‘sorted out’ before transmitting energy to the mainspring. This is particularly critical when small movements of the wrist translate into gentle back and forth rocking of the rotor. A good proportion of that gentle rocking is not actually doing anything apart from setting the reverser mechanism (whatever type it might be) ready for further rotation of the rotor which might not actually take place.

    A unidirectional winding system on the other hand, has no reverser mechanism. Whilst the rotor is moving in the non winding direction it is doing nothing for the mainspring (and we can hear it freewheeling); but the vast majority of energy from the slightest movement in the winding direction is transmitted efficiently – the dead angle is less and the mainspring is wound more.

    For those who are very active this is perhaps rather academic. I have always wanted to feel as confident in something that is purported to be doing ‘half a job’ as one which goes the whole way and Jaeger LeCoultre’s findings have allayed any fears I may have had; as reported in Watchtime Magazine:

    “We tested Caliber 899 in two ways, in the standard version with bidirectional winding and in an altered form with unidirectional winding. Unidirectional winding was significantly slower on the Cyclotest machines. But we also asked different people to wear these watches on their wrists. We gave them wristwatches with slack mainsprings and asked them to wear them from 8 a.m. to 4 p.m. On average, watches with unidirectional winding were twice as strongly wound as watches with bidirectional winding.”

    I decided to conduct my own experiment on the basis of the above. With the PRS-68 absolutely stopped, no power at all, I gently twisted it and tilted it back and forth for precisely three minutes. I didn’t put it on my wrist, just held it and moved it. It took almost all of those three minutes to get up and running but once the seconds hand was scurrying its way along, I set the watch back in the box and waited. From those three minutes of movement the watch ran for no less than 6hr 25min. Thus, it appeared that three minutes of movement gave me about one seventh of total power reserve! Very impressive. Next, I did exactly the same with a brand new Seiko 4R36 (bidirectional winding) equipped watch, moving the watch in very much the same way as the Smiths for the same amount of time – the Seiko ran for 3hr 55min. Whilst my little experiment wasn’t particularly scientific, it seemed to back up JLC’s findings and it has to be said, gives me great confidence in the Miyota 9015. It is more efficient than an equivalent mainstream Seiko movement – for me anyway. For those more active then the chances are that both systems are just about equal."

  13. #13

    Smiths PRS-68 on Ebay

    Smiths on eBay has been sold......


    Quote Originally Posted by seabiscuit View Post
    One on eBay now. With three days still to go the bidding has reached £470.

  14. #14
    Master
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    Quote Originally Posted by WatcherofTime View Post
    Smiths on eBay has been sold......
    Went for £575.

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