一 + MW + 一 + MW (one by one)

Day by day, cup by cup

• Repeat one / a一yī + measure word to mean "one … at a time".
• 一个yí gè一个yí gè = "one by one"; 一天yī tiān一天yī tiān = "day by day".
• The doubling spreads the action out, step by step.

one / a一yī + MW + one / a一yī + MW

• The repeated measure phrase = "one after another".

students学生xué shengone一个yí gèone一个yí gècome in进来jìn lái。

• 一个yí gè一个yí gèto come in进来jìn lái = "come in one by one."

Works with other measures

• 一步yī bù一步yī bù (step by step), 一年yī nián一年yī nián (year after year).

Recap

Read the full reference: HSK 4 grammar — Adverbs.