正在
zhèngzài
A photograph snapped in the middle of the motion
The picture A turning wheel caught by the shutter mid-spin and held still right there. 正在 is the photo taken mid-action; 已经 is the scene after the action ended.
Where the picture shows up in 正在
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the middle of a meeting
他正在开会，现在不能接电话。
tā zhèng zài kāi huì, xiàn zài bù néng jiē diàn huà
He is in a meeting and cannot take a call right now.
People talking around a table behind glass while a hand outside cups the receiver
The standard line for answering someone else's phone.
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the middle of a meal
我正在吃饭，一会儿打给你。
wǒ zhèng zài chī fàn, yí huìr dǎ gěi nǐ
I am eating right now, I will call you in a bit.
Chopsticks held in one hand while the other presses a phone to the ear
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the middle of a machine's work
电脑正在更新，请不要关机。
diàn nǎo zhèng zài gēng xīn, qǐng bú yào guān jī
The computer is updating, please do not power it off.
A progress bar half filled and a hand stopped short of the power button
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the middle of rain
外面正在下雨，带伞吧。
wài mian zhèng zài xià yǔ, dài sǎn ba
It is raining outside, take an umbrella.
Water running down a window pane and an umbrella held out in the hallway
Weather sits very naturally with 正在.
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the middle of a consultation
医生正在看病人，请坐下等。
yī shēng zhèng zài kàn bìng rén, qǐng zuò xià děng
The doctor is with a patient, please sit and wait.
A lit lamp above a closed consulting room door, a hand offering the corridor chairs
All of it in one picture
正在 is a photo snapped mid-motion. Snap the middle of a meeting and it becomes the reason a call cannot be taken; snap the middle of a meal and it becomes a promise to ring back. Snap the middle of a machine and it becomes a warning not to switch off; snap the middle of rain and it becomes advice to take an umbrella; snap the middle of a consultation and it becomes an instruction to sit and wait. 正 is 'right at that time' and 在 is 'inside it' — together they make the middle.