How is engagment worked out?

Had midwife this morning and she has written on my notes 4/5 on the engagement column does this mean baby is 1/5 engaged?
I cant remember with Crystal

I can't remember either.. sorry hun. such a long time ago.. xx

I always thought 1/5 meant the head still had 4/5 to go before fully engaged 🤔

But when my friend was expecting she said 1/5 meant the baby only had 1/5 left 🤔

On my green notes there are explanations of the engagement. The lower the number, ie 1/5 or 2/5, the more engaged baby is as it measures what they can feel above the pelvis rather than how much is in the pelvis. I hope this makes sense x