How to write decimal values in words
How do you read numbers like these?
0.12 "oh point twelve", "zero point one two", "zero and twelve hundreds"
And these ones?
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"point twelve" is not acceptable for a decimal, as it leads to confusion as to whether "point one" means .1 or .01. After the decimal point you read each digit individually, though with times you can adjust as there may be an implicit minutes for the later digits.
You can use oh for nought or zero if you think there will be no confusion between O and 0 and o; there might be with say a password.
The treatment of numbers in language is an interesting topic. In base 10, we have terms for numbers to the left of the decimal, according to the powers of 10 they represent: e.g., 496 is four hundred ninety-six. For numbers to the right of the decimal, however--and also for numbers in bases other than 10--there isn't special terminology, and we simply speak each digit individually.
Having said that, it may be worth noting that certain common decimal values can be conveniently represented as fractions, presenting an alternative for pronunciation. Here, the rule is to state the numerator as a standard integer but the denominator as an ordinal number--singular if the numerator is 1; plural otherwise. So one-third, two-fifths, etc.
In the case of the fourths, we have options: it's common to refer to 1/4 and 3/4 as one quarter, and three quarters, while one-fourth and three-fourths are equally acceptable. With 1/2, however, we have the maverick: the only acceptable term for this fraction is one-half, which does not use the ordinal number or anything else that remotely sounds like the word two.