Babel and the decimal separator

By dafault, spanish changes to a comma as decimal separator; to change to a dot, you can use \decimalpoint:

\usepackage[spanish]{babel}
\decimalpoint

This gives the possibility to revert at any moment to a comma, using \decimalcomma or even to select a different symbol with \spanishdecimal{<symbol>}

The package option es-nodecimaldot disbales completely this decimal separator mechanism and uses a dot,leaving without effect \spanishdecimal{<symbol>}, and \decimalcomma:

\usepackage[spanish,es-nodecimaldot]{babel}

The Spanish module does tricks to accommodate for traditional Spanish typesetting rules. One is to transform periods followed by digits into a comma in math mode. You can disable this behavior with

\usepackage[spanish,es-nodecimaldot]{babel}

There are many other options, you can find them by

texdoc spanish

or going to http://texdoc.net/texmf-dist/doc/generic/babel-spanish/spanish.pdf