Dear Bogdan,

I've followed up on your advise to edit

wp-content/plugins/wpdatatables/source/class.wpdatachart.php

wp-content/plugins/wpDataTables/assets/js/wpdatatables/wdt.chartJS.js and 

wp-content/plugins/wpDataTables/assets/js/wpdatatables/wdt.chartWizard.js 

As mentioned in : https://tmsplugins.ticksy.com//ticket/1755720/

I see there are issues with this approach:

When more than one line is plotted, the scaling of the Y-axis is subject to two scales instead of one. This means that values on the Y-axis do not correspond correctly with actual values of the lines. I noticed this when I use data has that one line with some strong negative outliers vs another line with similar shape, but less strong negative outliers. I see that the line with smaller values, but stronger outliers, is displayed above a line with lower values, but less strong outliers.

So: LineOne@0 = -100, LineTwo@0 = -50, LineOne@1 = 10, LineTwo@1 = 20 --> results in: LineOne displayed above LineTwo @ time 1. Which is incorrect.

When I click in the legend on one of the labels of the lines, the scaling of the Y-axis is fine.

I realized that this had to do with your suggestions, as this issue is not present when using the original files.

Unfortunately, that still doesn't solve the initial problem: Negative values are cut-off from the chart due scaling limited to 0. 

Example

The issue was that I had selected Stacked Area chart by accident. Apologies..!  Please close