On how double precision numbers are encoded in a pdf file

Imagine the following tikz/pgfplots code:

% compile as: lualatex --jobname=figname-f1 figname.tex
\documentclass[10pt]{book}
\usepackage{tikz}
\usepackage{pgfplots}
\pgfplotsset{compat=1.6}
\pgfrealjobname{figname}
\pdfminorversion=5
\pdfobjcompresslevel=6
\pdfcompresslevel=9
\begin{document}
\beginpgfgraphicnamed{figname-f1}%
\begin{tikzpicture}
\begin{axis}[width=14cm,height=6cm,scale only axis,axis lines=left,axis]
(8.27605704077856,0.505526531790625,1.15577754382534e-05)
(8.27605704077856,1.01105306358125,4.16291426502054e-06)
(8.27605704077856,1.51657959537188,3.77146738938349e-06)
.... % many more lines similar to the one above
};


This tex file is about 3Mb. Compile it to get figname-f1.pdf. Now replace by zero all the third components that are very small, ie:

\addplot3 coordinates{
(8.27605704077856,0.505526531790625,0)
(8.27605704077856,1.01105306358125,0)
(8.27605704077856,1.51657959537188,0)
.... % many more lines similar to the one above
};


This new tex file is about 2Mb. Compile it.

In the personal examples I am working on, the two .pdf files are of the same size, about 530kb. Is that expected?

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What's "1Mo"? WolframAlpha suggests 1 month, but I don't think the difference would be that big. – doncherry Oct 11 '12 at 4:49
Yes, that is to be expected, since these are just coordinates, and there is virtually no difference in the placement of the markers in those locations. The difference in the .tex file stems from the loss in characters. – Werner Oct 11 '12 at 4:49
What is 1Mo? Keep in mind that file sizes on computers are not continuous, they are usually in 4k chunks to optimize disk performance. So, if you are seeing size differences in the .tex (whcih are just plain text files) with such small changes then it is probably because you crossed this quantized amount. – Peter Grill Oct 11 '12 at 4:50
@Werner: ha yes I see, it is because points are then projected on the plane. Too bad. – pluton Oct 11 '12 at 4:56
@doncherry The French prefer to call them "mégaoctets" rather than "mebibytes" (or "megabytes") and I find this perfectly legitimate. It's futile, though, using a symbol which is not understood outside of France (this is not a rebuke to pluton, of course). By the way, the IEC proposed the symbol MiB, which is endorsed by IEEE and CIPM (source Wikipedia) – egreg Oct 11 '12 at 9:32