There are additional options available. to rpm which are detailed in the rpm(8) man page. The contents of the rpm(8) man. page should be thoroughly understood by the System Administrator. Return to: RedHawk Linux Frequently Asked Questions.
You can assess a fever based on symptoms without a thermometer while also looking at potential causative factors. So things to look out for are feeling extremely hot causing whole body sweats, followed by feeling insatiably cold, requiring layers of bedding and experiencing whole body shaking (rigors).
With your homemade thermometer you aren't actually measuring temperature, just seeing temperature changes. If you have a real thermometer, you can use it to make a scale on your homemade thermometer: let your bottle get to room temperature and then mark the straw with what the actual room temperature is. Then set the bottle in the sun and do the same.