Tummy Measuring question

I went in for my 32 weeks doctors appointment today and measured 32 cm. My doctor said my last visit (30weeks) I was measuring at 28cm which caused him to be a bit concerned. However, this appointment, I’ve caught up and am measuring right on 32cm at 32 weeks and he said he’s no longer worried. I read online it’s normal to be either 2cm under or 2cm over. For example, if I’m 32weeks, my measurements would be considered normal if it falls within 30cm-34cm. Is it true? And What is everyone measuring ?