Truncature?

Hello,

Here a set of data (file.asc)

0 34.42904
1 34.42924
2 34.42965
3 34.43026
4 34.43106
5 34.43207
6 34.43329
7 34.43469
8 34.43632
9 34.43814
10 34.44017

I wish to fit them with
dep (x, a) = x * a

I can do
1) 
fit Off + dep (x, slope) "file.asc" u ($1*($1+1)):2 via Off, slope
and I get
final sum of squares of residuals : 2.94071e-10
Off            = 34.429           +/- 2.581e-06    (7.496e-06%)
slope           = 0.000101126      +/- 4.802e-08    (0.04749%)

with
Off = 34.429039486

2)
set table $DATA; plot "file.asc" u ($1*($1+1)):($2) "%lf %lf" with table ; unset table
fit Off + dep (x, slope) $DATA u 1:2 via Off, slope
and I get
final sum of squares of residuals : 1.36307e-08
Off            = 34.429           +/- 1.757e-05    (5.103e-05%)
slope           = 0.000101045      +/- 3.27e-07     (0.3236%)

with
Off = 34.4290491247


Option 1) is correct, but not option 2)

Why?

Thanks

===========================================================================
 Patrick DUPRÉ                                 | | email: [email protected]
 Laboratoire interdisciplinaire Carnot de Bourgogne
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