title: How to interpret ACF plot y-axis scale in R
body: <p>I have created a zoo time series object for a subset of data that I have.  The data is evenly spaced in hourly intervals but it is a weakly regular time series according to the R-zoo documentation (ie. there are some time points that are missing in the data)</p>
  
  <pre><code>df &lt;- read.table("Desktop/AutoCorrelation_hourly_testdata.csv", header = TRUE, sep = ",")
  sub &lt;- df[df$sid == 59, ]
  sub &lt;- sub[!duplicated(sub[c("binstart_date", "binstart_time")]), ]
  library(zoo)
  z &lt;- read.zoo(sub, sep = ",", header = TRUE, index = 1:2, tz = "", format = "%Y-%m-%d %H:%M:%S")
  acf_C_duration = acf(coredata(z$C_duration), na.action = na.pass, plot = TRUE)
  </code></pre>
  
  <p>I get the following plot: </p>
  
  <p><a href="https://i.stack.imgur.com/bNX50.png" rel="nofollow"><img src="https://i.stack.imgur.com/bNX50.png" alt="enter image description here"></a></p>
  
  <p>My question is what exactly is the scale of the lag on the y-axis if my data is in hourly intervals?  What would be the best way for me to interpret this plot?</p>
  
  <p>I'm not that experienced with statistics or R, but I am trying to determine if this data set seems to follow a rhythm or have any underlying pattern/periodicity.  From researching online it seems as though the R autocorrelation function could do this for me. If you think I should be using any other method please let me know.</p>
  
  <p>Thanks!</p>