八成 ba1cheng2 (80 percent!)
Many people will be very familiar with 成 chéng, mainly from its meaning 'to be become [something]', but did you know that it means 10 percent?
People commonly rate their mobile phones on a scale from 五成 (50 percent) 到十成 (100 percent) based on how old they are. Less than 五成 is 旧 (don't bother measuring it.) My phone is 旧.
So, 成人，Q: 你的手机多久？。。。A: 八成。
Well, I don't think that it is hard science, but if you have a flash new expensive phone you would describe it as 八成 or 九成; in China if it is a couple of years old it is probably 五成 or 六成。 :)
Mine is old technology so it is just 旧。
Thanks for the movie reference: in what context did they use it??
Ah OK I was misunderstanding. So it‘s not about how long we’ve had and been using our smartphones, but about how new/old the model is.
I linked to my own comment, but Trevorb gives the context in his original post.