service/prometheus.md

@@ -654,7 +654,7 @@ built-in threshold:
     (time() - apt_package_cache_timestamp_seconds)/(60*60) > 24
 
 What this does is calculate the age of the package cache (given by the
-`apt_package_cache_timestamp_seconds` metric) by substracting it to
+`apt_package_cache_timestamp_seconds` metric) by subtracting it to
 the current time. It gives us a number of second, which we convert to
 hours (`/3600`) and then check against our threshold (`> 24`). This
 gives us a value (in this case, in hours), we can reuse in our