Sum of two resulting tables

[pierromond]

Discussed in #601

^{Originally posted by kaasym July 30, 2023}
Hi, I have a request. Would it be possible to improve the program by the sum of two resulting tables? And the same for isolins? I need to add two results, one for line noise sources and the other for point noise sources. For a few points I can add it in Excel, but I can't do a bigger area. Especially for isolins. Thank you. Jirka