What does the point in the middle between two numbers mean?
Short answer

It's a decimal point.

Longer answer

A point in the 'middle' of the neighboring characters is called an interpunct, and was the standard in UK typography for marking a decimal at one point in time (possibly elsewhere as well). You're most likely to encounter it in older issues in UK and UK-inspired journals, and no doubt some have lagged behind the trends for reasons of tradition/stubbornness or whatever else and still use it.

Note that you will also encounter countries that use the comma as a decimal separator; Wikipedia has a list that includes most of mainland Europe and South America, for example.