I’ve been charting my BBT every morning before getting up, someone on here thought based on my chart that my thermometer may have been low on batteries or just a bad one so I got a another new bbt thermometer and just to compare I sat down and took my temp with both. Thermometer A (my original new one) read 99.21 and thermometer B (second one I got) read 99.03

After that I retested with the one I just got and it read 99.17..... I am officially confused and extremely frustrated with which thermometer is accurate?!?!! Should I stick with the one I’ve been using or does anyone have suggestions on one? The first one I got is from CVS and the second is from Target