title: Addition in hexadecimal
body: <p>I may formulated the question a bit wrong. I need to calculate the IPv4 header checksum in hexadecimal with paper and pen. At this link <a href="http://en.wikipedia.org/wiki/IPv4_header_checksum" rel="nofollow">http://en.wikipedia.org/wiki/IPv4_header_checksum</a>
  on the last example they do it. </p>
  
  <p>I have a bit of problem understanding how they count directly in hexadecimal. When doing it on paper what if I get a number over 15 for example 48 what reminder will I use and what will I write down?</p>
  
  <p>Anyone that can explain how to handle this?</p>
  
  <p>Thank you and sorry for formulating the question wrong but I have changed it now:)</p>