It is very surprising that
set(handles.edit1, 'String', x)
shows any string at all, when x is a double value. Actually only strings and cell strings are accepted.
This shows x with 16 digits:
x = -0.134635523018792;
set(handles.edit1, 'String', sprintf('%.16g', x))
Note that it cannot be guaranteed, that you see "all" digits, because there are no accurate decimal representations for the numbers, which are store in binary format internally. See also: FAQ: Why is 0.3-0.2-0.1 ~= 0
