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I want to increase the precision globally to 50 at least, but $MinPrecision does not work.

$MinPrecision = 50;
x = Sin[2.]
(* -> 0.909297 *)

Precision[x]
(* -> MachinePrecision *)

How to set the working precision globally, i.e., make all the calculations in the notebook use the new precision?

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    $\begingroup$ Hope this helps, have a look at: mathematica.stackexchange.com/questions/6421/… $\endgroup$ – Kardashev3 Dec 1 '13 at 17:15
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    $\begingroup$ Precision settings only apply for arbitrary-precision values. When working with machine numbers, there is no tracking or adjustment of precision. So, enter your value as e.g. 2.`16 rather than 2. and you will get the effect you are after. $\endgroup$ – Oleksandr R. Dec 1 '13 at 17:27
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    $\begingroup$ My notebook involves machine precision numbers in many places; it would be tedious if I do the change like 2.`16 in every place. Is there a convenient way to set the precision once and for all? $\endgroup$ – renphysics Dec 1 '13 at 19:03
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This looks like a duplicate of my question here Global precision setting . Since I formulated it in a slightly different way, coming from Maple it might however be worth quoting the answer given by Mr. Wizard here. It worked for me in Mathematica 9 if there are no arbitary precision numbers in the notebook (defined as e.g. 2.`16):

$PreRead = (# /. 
 s_String /; 
   StringMatchQ[s, NumberString] && 
    Precision@ToExpression@s == MachinePrecision :> s <> "`50." &);

3/1.5 + Pi/7

Precision[%]

This will act on all later commands before the actual command is executed and set the precision of contained numerical values to 50 digits.

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