# Value difference between OPC Kepware and readBlocking

**URL:** <https://forum.inductiveautomation.com/t/value-difference-between-opc-kepware-and-readblocking/89531>\
**Category:** Ignition\
**Created:** [April 26, 2024, 2:43pm UTC](https://forum.inductiveautomation.com/t/value-difference-between-opc-kepware-and-readblocking/89531 "2024-04-26T14:43:34Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![grzegorz.kaczmarczyk](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/grzegorz.kaczmarczyk/32/24167_2.png) [@grzegorz.kaczmarczyk](https://forum.inductiveautomation.com/u/grzegorz.kaczmarczyk)\
**Post date:** [April 26, 2024, 2:43pm UTC](https://forum.inductiveautomation.com/t/value-difference-between-opc-kepware-and-readblocking/89531/1 "2024-04-26T14:43:34Z")

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Hi,

Why there is a difference in value tag between OPC Kepware and the value read by the function readBlocking? Also, the value in the Designer is exactly like in the OPC.

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/2/0/20dbf5bc3a54011e1ec0183d8116de1a83b0791a.png)

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<div class="post-metadata">

**Author:** ![grzegorz.kaczmarczyk](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/grzegorz.kaczmarczyk/32/24167_2.png) [@grzegorz.kaczmarczyk](https://forum.inductiveautomation.com/u/grzegorz.kaczmarczyk)\
**Post date:** [April 26, 2024, 3:09pm UTC](https://forum.inductiveautomation.com/t/value-difference-between-opc-kepware-and-readblocking/89531/2 "2024-04-26T15:09:51Z")

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And also:

 ![image1](https://us1.discourse-cdn.com/inductiveautomation/original/3X/0/0/00ae210c8d632eaa687594768db9c8a1219da8e3.png)

Why round 5 gives us 27,8 and changing it to 6, immediately gives us 27,799999?

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**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\
**Post date:** [April 26, 2024, 3:18pm UTC](https://forum.inductiveautomation.com/t/value-difference-between-opc-kepware-and-readblocking/89531/3 "2024-04-26T15:18:12Z")

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> [@grzegorz.kaczmarczyk](#):
>
> Why round 5 gives us 27,8 and changing it to 6, immediately gives us 27,799999?

standard python behavior: [Built-in Functions — Python 3.12.3 documentation](https://docs.python.org/3/library/functions.html#round)

```python
>>> round(27.799999, 5)
27.8
>>> round(27.799999, 6)
27.799999
>>>

```

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**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [April 26, 2024, 3:28pm UTC](https://forum.inductiveautomation.com/t/value-difference-between-opc-kepware-and-readblocking/89531/4 "2024-04-26T15:28:27Z")

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For 32-bit floating point, `27.8` _ **IS** _ the **same number** as `27.799999`.

Nothing to do with Ignition **at all**.

The least common denominator of any number ending in `.8` is **five**. Which yields a repeating binary fraction.

{ If you convert to double, and show even more decimal places, it will look even weirder. Simply artifacts of binary fractions. }

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**Author:** ![Felipe\_CRM](https://avatars.discourse-cdn.com/v4/letter/f/dfb087/32.png) [@Felipe\_CRM](https://forum.inductiveautomation.com/u/Felipe_CRM)\
**Post date:** [April 26, 2024, 3:39pm UTC](https://forum.inductiveautomation.com/t/value-difference-between-opc-kepware-and-readblocking/89531/5 "2024-04-26T15:39:05Z")

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To illustrate Phil's point:

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/b/6/b64b2133e7ea8ebeb07c52918ef1b3b94fc2f818.png)  
([IEEE-754 Floating Point Converter](https://www.h-schmidt.net/FloatConverter/IEEE754.html))