one airpod is not charging - Gadget Link
One-to-one is used when you talk about transfer or communications. You may use one-to-one when you can identify a source and a destination. For eg., a one-to-one email is one sent from a single person to another, i.e., no ccs or bccs.
Understanding the Context
In maths, a one-to-one mapping maps one element of a set to a unique element in a target set. One-on-one is the correct adjective in your example. See Free ... Some people say a dog=one, dogs=ones, the dog=the one=that, and the dogs=the ones=those.
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Key Insights
It's a rule of thumb, but what I found was that this is not always correct. 101: One hundred and one 234,500: Two hundred and thirty four thousand five hundred Based on my experience, Britons, Australians and New Zealanders say the "and", and North Americans do not (ie "one hundred one", etc). I believe most other English speaking countries say the "and". Which version was used first?