Please take some time to state your question.
What part of the previous answers do you not understand?
When inputing numbers, Excel will only interpret the first 15
significant digits. Any remaining digits will be treated as zero.
So 1234567890123456 will be interpreted as 1234567890123450. Now
that ...56 is __not__ rounded to ...60.
There are only two ways to avoid that; both force Excel to treat the
numeric string as text, not a number. The two ways are:
(a) Format the cell as Text before entering the data; or
(b) Enter the data prefixed with an apostrophe (aka single-quote).
For example, '1234567890123456.
This will not get you more precision if you reference the text in an
arithmetic expression. For example, if A1 contains the text
'1234567890123456, =A1*2 results in the number 2469135780246900, not
2469135780246912.
Note: Contrary to a previous comment, you __can__ refer to a numeric
string (text) in arithmetic expression. However, some Excel functions
will still treat it as text. For example, =A1+A1 results in the
number 2469135780246900, but =SUM(A1,A1) results in zero. Moreover,
the numeric string (text) will be treated as text in comparision. For
example, =A1>1E+300 returns TRUE because in Excel, text is always
considered greater than numbers.
Consequently, it is best not to expect to use numeric strings (text)
as numbers in expressions. This form should be used for "numbers"
that are actually identifiers, e.g. account numbers.