Fluid check, second time moms+

I am a second time mom but never had to go for a fluid check with my first! I am due Monday and baby is still high. I am 2 cm dilated and 50% effaced but have been since 36 weeks! So we scheduled my induction for July 10th(my dr won't do it before I'm 41 weeks). They are sending me Tuesday for an nst and a fluid check. I am familiar with nst's because I had a few with my first but don't think I did a fluid check, any one know what the fluid check includes?