title: Ticks between Unix epoch and GPS epoch
body: <p>What is the number of one second ticks between Unix time epoch (01 Jan 1970) and GPS time epoch (06 Jan 1980)?</p>
  
  <p>I have seen multiple answers from several sources on the web. One camp claims the answer is <strong>315964800</strong>, the other claims it is <strong>315964819</strong>. I always thought it was 315964800, but now am not so sure.</p>
  
  <p>I just found my software baseline has been using 315964819 for the last eight years. I have a hard time understanding how it could have been 19 seconds off and no one noticed it when we integrated our embedded devices with other devices.</p>
  
  <p>I think that whoever put 315964819 in the code baseline must have mistakenly used a TAI offset (19 seconds).</p>
  
  <p>From what I understand, Unix time does not include leap seconds, which would indicate to me that 315964800 is the number of ticks between the two epochs. Then I think about how Unix time handles the leap second. It simply repeats the tick count when there is a leap second inserted, and there <em>were</em> 19 leap seconds inserted between 1970 and 1980... I start to wonder if the repeated ticks matter. I do not think so, but someone in this code's history thought so, and it seemed to work....</p>
  
  <p>The long and short of it is I am about to change a constant set in the dark ages of this product that has to do with timing, which is important for the platform, from what it had been to what I believe is more accurate, and I wanted some sort of thumbs-up from more knowledgeable people than me.</p>
  
  <p>Can someone authoritative please step in here?</p>
  
  <p><a href="https://www.google.com/#q=315964800">315964800 camp</a></p>
  
  <p><a href="https://www.google.com/#q=315964819">315964819 camp</a></p>
  
  <p>Also note that I'm only asking about Unix epoch to GPS epoch. I'm pretty sure we've got leap seconds since GPS epoch covered appropriately.</p>