How much variation in BBT?

Hi everyone
​So I just started taking my bbt in the mornings...
​I am on my period so obviously not ovulating (!) but I have noticed there seems to be a fair bit of variation in my temperature. Up to 0.5 degrees C. Is this normal or is my thermometer broken or something?
​Obviously I need my thermometer to work to get accurate readings when I DO ovulate. 
​Any advice? 

Glow Resources

Let’s Glow

Glow is here for you on your path to pregnancy

Glow helps you navigate your fertility journey with smart tools, personalized insights, and guidance from medical experts who understand what matters most.

25+ million

Users

4.8 stars

200k+ app ratings

20+

Medical advisors