Hosting companies proclaim amazing site uptimes but do they really mean anything. Recently I had cause for concern as to the accuracy of the quoted percentages and I wanted to check for myself the uptime of two different hosts. To keep a check on two different hosting accounts use the following script. I placed this script on my own computer (localhost) and let it run in the browser 'localhost/uptime.php' The script checks a website placed on each host and writes the response to uptime.txt I set the page to refresh 900 seconds (15 minutes).
You will need a local server to be installed on your computer to run this script on your own localhost, (XAMPP or LAMPP). There are alternatives do a search for "site uptime" and you will find companies which will do it for you and send you an email if your sites are down. But writing code is the best way to open your world and let you take control.
Do the maths. 99.9% means that they can still be in there guarantee with quite a lot of down time. 365.25 days times 24 hours = 8766 hours in a year, times 60 minutes = 525960 minutes in a year. Now divide that by 12 we get 43830 minutes in a month. 99.9% uptime means that there is still 0.1% acceptable downtime 0.1% = 43830 divided by 1000 gives us 43.83 minutes down time every month so just short of 3/4 of an hour. That does not include 'Scheduled Maintenance'.