How do I display more digits of numeric results?
Standard decimal numbers in the Wolfram Language are internally represented with machine precision*:
In[1]:= $MachinePrecision
Out[1]= 15.9546
The InputForm of a given number displays all available digits:
In[2]:= InputForm[200./7]
Out[2]//InputForm= 28.57142857142857 
Yet by default, only six digits of such machine-precision numbers are shown:
In[3]:= 200./7
Out[3]= 28.5714 
More digits can be displayed either for an individual number or all machine-precision numbers.
Individual Number
NumberForm displays the desired number of digits of a particular number:
In[4]:= NumberForm[200./7, 12]
Out[4]//NumberForm= 28.5714285714 
NumberForm cannot return more digits than the number has:
In[5]:= NumberForm[200./7, 24]
Out[5]//NumberForm= 28.57142857142857 
All Numbers
- Navigate to the menu item Edit ▶ Preferences on Windows or Mathematica ▶ Preferences on Mac.
 - Select the tab Appearance ▶ Numbers ▶ Formatting.
 - In the line “Number of digits displayed in output”, set the preferred precision.

 
* It is of noninteger value since the precision of a number is defined in terms of the logarithm of the uncertainty in the corresponding exact value.
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