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Metric Rounding Error

Discussion in 'Woodturner PRO Support Forum' started by KenM, Mar 21, 2017.

  1. KenM

    KenM New Member

    So, being the sadist that I am, I designed a closed-segment feature ring using 80 segments. I cut a template for my sled, and proceeded to cut the 80 pieces. I used the instructions from WTP for the measurements, of course.

    I assembled the ring, and it went together perfectly - gotta love that wedgie sled! Based on previous success with WTP, I didn't bother measuring the ring to see if it was the right dimensions - it's worked before, up to 48 segments (although a comment on that in a moment).

    I assembled the ring, and just now I went to place it on the bowl, the wouldn't you know, it was substantially smaller that the diameter of the bowl itself. WTF?

    Before I go any further, be advised that I use metric for dimensions. I can't stand fractional measurements, and for most of what I do, metric measurements work perfectly.

    WTP indicated a segment length of 7mm, and with 80 segments you end up with a circumference of 189mm. This is incorrect. The actual measurement should be 178mm. This is a substantial difference. The correct segment length should have been shown as 7.4mm.

    The end-result is that the ring is too small, and is unusable. No big deal, it's just wood and time, but still a bit annoying.

    So, I do have a request - would it be possible to have a point release that would change the segment report and the ring report to use fractional metric measurements when metric units are selected? I'm thinking to 1/10th (ha! ya see what I did there?) of a mm would be sufficient.

    If that isn't possible, then I guess I switch back to Imperial, which has the option of decimal measurements.

    Regarding the 48 segment ring, I did notice that it was a bit smaller than it should have been, but I chalked that one up to setting up the jig incorrectly. It was just slightly smaller, so the ring was still usable.

    Thanks Lloyd!
  2. Lloyd Johnson

    Lloyd Johnson Administrator Staff Member

    All measurements that are stored in the database are stored in decimal inches. This means that when you select metrics, all I have to do is use very simple conversions to display the decimal inch in millimeters. The process begins by calculating the diameters, both inside and out, of each row. I then work backwards using the same formulas that I've always used in Woodturner PRO to arrive at the imperial decimal Segment Edge Length. I then use Woodturner PRO to verify that the same diameters generate the same Segment Edge Length in both programs which I have already done on a dozen occasions.

    I do not use fractions for a very good reason. In the next few years, keyboards will become optional as all new monitors are touch screen. More and more, laptops will become pads and keyboards will become digital and on-screen as opposed to detached analog devices. This means that all controls will have to be numeric because those can be incremented by clicking an up/down arrow with a finger or stylus. Fractions are always text entries and cannot be used in a numeric field. I'm afraid I don't understand what you mean by fractional metrics. I can change the number of decimals but fractions of metrics makes my teeth itch - never a good sign.

  3. KenM

    KenM New Member

    Perhaps it's poor wording on my part.

    My requirement is as follows: when "metric decimal millimeter" is selected as the Numeric Display setting, I would like to see segment measurements expressed down to 1/10th's of a mm accuracy, specifically the segment length. The other segment measurements are less important, and likely do not need this level of accuracy.

    As an example, if I have a 80-segment ring that has an outside diameter of 189mm, then the segment length should be displayed as 7.4mm, rather than 7mm as it currently does. Reversing this calculation, 7.4mm would give an outside diameter of 188.43mm, which is close enough to 189mm. A 7mm segment length in a 80 segment ring yields an outside diameter of 178mm, which is not even close to 189mm. That's an error of 0.42", which is far too large.

    Hope that's clear.
  4. Lloyd Johnson

    Lloyd Johnson Administrator Staff Member


    I will be able to convert mm to mm with a trailing digit. Would you prefer two digits or is that more precision than would be useful?

    Timing is a bit of an issue, though, because the change in the Summary Grid is only half done and I can't post the next upgrade until that is complete. Until then, it will be best to switch to decimal inches and then just convert the value to mm with whatever precision you need.
  5. KenM

    KenM New Member

    Two extra digits of precision would certainly be overkill - one extra digit will be just fine.

    1/100" (imperial decimal precision) is equivalent to 0.254mm, so adding one extra digit of precision will put the metric measurements in the same ballpark as, but slightly more accurate than the imperial decimal measurements.

    No worries on the timing - I can switch to Imperial.

    Thanks for being so responsive, Lloyd!

    (FYI, the same changes should apply to Segment Pro, I would think)
  6. Lloyd Johnson

    Lloyd Johnson Administrator Staff Member

    You'll be happy to know that I've made the change to show millimeters with a single decimal digit. As soon as I can post the new build, it will be available.

  7. KenM

    KenM New Member

    Good news Lloyd, thanks!

    And thanks for the rapid turnaround - it's nice to see that customer service still exists!
  8. KenM

    KenM New Member

    Hey there Lloyd, was just checking in to see when you're planning on a new release of WTP...
  9. Lloyd Johnson

    Lloyd Johnson Administrator Staff Member


    I know I made the change you requested, but I cannot see where I made a new build. The date of my last post was the day I turned 65, and that probably explains why I completely spaced out about making a new build and I never thought any more about it.

    I've made myself a note to work on this tomorrow (Sunday) and as long as I don't misplace the note, it should be finished and I'll let you know that you can download it.

    Sorry about that.
  10. Lloyd Johnson

    Lloyd Johnson Administrator Staff Member


    Since it was such a nice day yesterday, we went on a long hike instead of working on the software. I will get back to it again today, but I am unclear on some things. I know you want metrics with a single digit but it is unclear to me if that is for WTP or SegPro. I said I had been making changes which is true, but my changes were in Segment PRO. All of your references are to WTP, however, but I will not be able to accomodate that at this time. WTP was written 16 years ago in C++ with Microsoft Foundation Class extensions and Microsoft no longer allows that to be compiled in the new Visual Studio Development platform. I do have a way of having work done on it, but I have to send the code to a 3rd party who can make changes and send it back to me. There is a minimum $1000 charge for this and since you can switch to decimal inches to get the accuracy you need, I won't be spending that money. When (and if) it becomes necessary to make more substantial changes to WTP, I'll add this request to the work order.

    Making changes in Segment PRO with regards to decimal metrics has its own challenges as I have found out the hard way. When I switched to creating the Summary Page as a spreadsheet and converted all the fields from text to numeric, the software in certain countries like France started aborting because of the culture requirements of the country. I had to switch some values back to text in order for the software to run in those countries. Until I can make a new virtual computer running French culture (not sure how I'm going to do this), I have no way of testing the changes and I haven't had time to research this.

    Since I have a lot of business travel coming up, I'm reluctant to make changes that may caus
  11. Bob Beaupre

    Bob Beaupre Super Moderator Staff Member

    Lloyd is that Microsoft Visual C++ 6
  12. Lloyd Johnson

    Lloyd Johnson Administrator Staff Member

    Yes, but C++ is not the issue. Using MFC has created the biggest challenges since that is no longer supported by Microsoft.
  13. Bob Beaupre

    Bob Beaupre Super Moderator Staff Member

    So what language is Segment PRO written in?
  14. Lloyd Johnson

    Lloyd Johnson Administrator Staff Member

    I wrote it in C# and use some customized 3D libraries.
  15. KenM

    KenM New Member

    I'm using WTP; while Segment Pro is the newer tool, I simply prefer WTP for the flexibility. So the fact that WTP is, effectively, at its end-of-life is somewhat unfortunate. I do understand the issues that you raise, however (I'm a software developer myself).

    That said, I can still using imperial decimal (blech) measurements :)

    I started working on a new bowl today, and I'm only getting two decimal positions in the summary report for edge length - I thought that there was three decimal positions in a previous report. Now, it has been a while since I've used the tool, so perhaps I'm not remembering correctly (likely!)

    I am running the most current version of the tool.
  16. KenM

    KenM New Member

    Hmm, methinks I was thinking of another tool that went to three decimal places :)
  17. Lloyd Johnson

    Lloyd Johnson Administrator Staff Member

    I'm afraid so. I haven't touched the reports system of Woodturner PRO in a number of years.

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