Understanding a diff file

Hi folks,

I am having difficulties in understanding diff file.
I would like to know what the following means in a diff file

ex:
202a251,253
1,102c120,126

I believe 'a' will be 'append'. Line 202 appended to line 251. but why there is 253 ???.

Like the above if any one can tell me how to understand these, it will be helpful.

Any links to useful websites that explains how to interpret diff file will be also enough. thanks. :confused:

Perhaps try sdiff

Comparing and Merging Files