Message and negative value

Hello
The calculation is used in the form. The final value can be negative.
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Please inform how to display an information message if the value is negative.
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Thanks a lot

1) PHP action

return ($this->data("name of value", "default") < 0);

2) Event switcher, data source {var:switchname} , events true, false

Unfortunately it did not work out
Tell me what's wrong

Well is your data field actually called "T" ?

Yes

Try 1,0 or {value:true},{value:false} instead of true,false
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And check your debug action to make sure T is returning what you want it to.