This is a known issue that is hard to fix unfortunately. See also the documentation with suggested workarounds:
https://docs.octave.org/interpreter/Precision-issues.html

Closing as duplicate of bug #32980.

load('data');

plot(data(1:500,1),data(1:500,2),'-+')

The + markers show the real data. The line drawn is very coarse and doesn't match the markers. See course-plot.png. Line is the same when only line drawn.


If you make X values smaller graph is less coarse but if you zoom in the markers are still not on the line.
plot(data(1:500,1)-7e5,data(1:500,2),'-+')

zooming in with the full data set and markers is also around 20 seconds.

Initially seen with Octave 6.4.0 on Fedora Core 35. Installed the 7.2.0 Anaconda version to test and got same behavior.

Large X values are datenum values. Same behavior seen when X is set to datetick('mm/dd/yy')