xpost: calling all BBT experts: thermometer question

[Hope4More]

Hi! I need help even though I've been doing BBT since, oh, 2009

I've been using a BBT from CVS - a white one with a pink tip. Worked great through my last cycle, and this cycle it's been wonky (although so has my body!). My last three temps were all EXACTLY 97.45 (which were supposed to be my ovulation temps, so I don't know where that puts me now...). I thought maybe my thermometer was bad, but later in the day gave me a different temp, so it's not STUCK on 97.45.

I went to CVS and bought a new one. It's purple. I thought I'd take my temp on both to see if I get similar readings (not the same, but it should be in the same ballpark, RIGHT?). The old thermometer comes back at 96.78. The new thermometer comes back at 97.33. I cross checked it with a fever thermometer (which is only valid to two tenths, but it would tell me which one was right), and it came back 97.5. soooo... is the old one wonky? But the bigger question is, do I start charting with the new one? I'm already on day 22, no o in sight, although all signs pointed to an O within the last 3 days or today. I think this means my WHOLE chart is going to be off, which wouldn't be that big of a deal if I had normal cycles, but I don't. I go from 25 days to 72... I guess i'm asking what would you do?