# Error\_ExpressionEval not allowing me to keep summing values

**URL:** <https://forum.inductiveautomation.com/t/error-expressioneval-not-allowing-me-to-keep-summing-values/91042>\
**Category:** Ignition\
**Created:** [May 28, 2024, 10:41pm UTC](https://forum.inductiveautomation.com/t/error-expressioneval-not-allowing-me-to-keep-summing-values/91042 "2024-05-28T22:41:02Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Marty\_Malone](https://avatars.discourse-cdn.com/v4/letter/m/858c86/32.png) [@Marty\_Malone](https://forum.inductiveautomation.com/u/Marty_Malone)\
**Post date:** [May 28, 2024, 10:41pm UTC](https://forum.inductiveautomation.com/t/error-expressioneval-not-allowing-me-to-keep-summing-values/91042/1 "2024-05-28T22:41:02Z")

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I am using an expression tag to sum the value to 4 tags from 4 different PLCs. If any of the PLCs is not connected, then I get this error "Error\_ExpressionEval" Which turns the cell red and doesn't keep summing the other values. Is there a way I can give a default value of zero of the value of the last tag read when one of the PLCs is not connected or turned off? This way I can continue to monitor the overall production of the other PLCs.

![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/3/8/381085a60bc91c120a199513430d42f1936b9c1e.png)

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<div class="post-metadata">

**Author:** ![paul-griffith](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/paul-griffith/32/37249_2.png) [@paul-griffith](https://forum.inductiveautomation.com/u/paul-griffith)\
**Post date:** [May 28, 2024, 10:47pm UTC](https://forum.inductiveautomation.com/t/error-expressioneval-not-allowing-me-to-keep-summing-values/91042/2 "2024-05-28T22:47:35Z")

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Possibly via [`try`](https://www.docs.inductiveautomation.com/docs/8.1/appendix/expression-functions/logic/try), but we'd have to see your expression to be sure.

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<div class="post-metadata">

**Author:** ![Transistor](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/transistor/32/3380_2.png) [@Transistor](https://forum.inductiveautomation.com/u/Transistor)\
**Post date:** [May 28, 2024, 10:54pm UTC](https://forum.inductiveautomation.com/t/error-expressioneval-not-allowing-me-to-keep-summing-values/91042/3 "2024-05-28T22:54:27Z")

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```python
if(isGood({[default]tag0}), {[default]tag0}, 0)
+
if(isGood({[default]tag1}), {[default]tag1}, 0)
+
...

```

Does that do what you want?

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<div class="post-metadata">

**Author:** ![Marty\_Malone](https://avatars.discourse-cdn.com/v4/letter/m/858c86/32.png) [@Marty\_Malone](https://forum.inductiveautomation.com/u/Marty_Malone)\
**Post date:** [May 28, 2024, 11:15pm UTC](https://forum.inductiveautomation.com/t/error-expressioneval-not-allowing-me-to-keep-summing-values/91042/4 "2024-05-28T23:15:41Z")

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I will try this and see.