There is no excuse for a chart to invent data points that never existed in your table, and the fact that Excel does this without warning is a genuine problem. The student who posted this is not misreading the graph or making a simple formatting mistake; they are watching a line bend toward coordinates like 2364;11 when the actual table clearly shows 2359;11. That is not a rounding quirk or a visual illusion. That is Excel quietly manufacturing phantom values and passing them off as your data.
The practical takeaway is uncomfortable but necessary: when Excel builds a chart, it is not always plotting what you think it is plotting. In this case, the line for that specific series is likely set to a chart type that interpolates between points using a method that does not match your raw numbers, or the axis is treating your X values as a continuous category rather than discrete labels. The result is a line that dips and spikes at coordinates that exist nowhere in your spreadsheet. If you are a student, a researcher, or anyone who has ever submitted a graph with a deadline looming, this is the kind of bug that costs you marks, credibility, or worse, a conclusion built on a shape that was never really there.
The fix is not to abandon spreadsheets or to assume every graph you make will betray you. The fix is to check your chart's underlying data source, confirm that the X and Y ranges are correctly assigned, and switch the chart type for that series to a simple straight line or scatter plot with connecting points that match your table exactly. You can also right-click the problematic series, select "Format Data Series," and ensure that "Smooth line" is off and that gaps are handled as gaps, not as interpolated values. If your chart still insists on inventing coordinates, delete that series and rebuild it from scratch using the specific cells you want plotted, nothing more, nothing less.
What this student experienced is not a failure of their understanding; it is a failure of the tool to be transparent about what it is doing. The graph should serve the data, not the other way around. So before you hit submit, right-click that chart, look at the actual data ranges, and ask yourself if the line in front of you matches the numbers you typed. If it does not, trust your eyes, not the default settings. And if you are the one helping a friend at 11 PM the night before a deadline, tell them to check the chart type first. It is not glamorous, but it is the difference between a graph that tells the truth and one that quietly lies.