[solved] Calc shows no chart

I select two columns for the XY data and insert graph.
But it shows nothing (just a white rectangle, with nothing inside).
Chart type doesn’t matter.

LibreOffice Version:
Build ID: 1:5.1.4-0ubuntu1~trusty1
CPU Threads: 4; OS Version: Linux 4.4; UI Render: default;

Is it numeric data, or perhaps numbers entered as text?
Can you post an example?

You’re right, it was actually numbers entered as text. I’ll add “solved” to the question but I describe my case here in case another user finds it useful. I was searching for data in a website and downloaded a CSV file, which was opened using calc. So in my screen I was seeing a spreadsheet with numbers. That is why I was confused when trying to plot the values. But yes, as mark_t says, the numbers were actually text. So I had to convert everything to numbers and then it worked just fine. Thanks