Temperature curve - explanation needed

Dee • 42, happy mother of a lovely boy through ICSI on 3rd round. TTC #2 since June 17
Hey girls! Can any of you explain the temperature curve to me using Celsius? 
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​- What is considered high/low temperature in Celsius (as far as fertility is concerned if course :) ) 
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​- What does a high/low temperature tell me about what's happening in my body?
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​- What clues should I be looking for?!