What is the correct expression about Units digit? (revised)

Question

I want to express it accurately.

For example, consider $1872_{(9)}$. I would like to refer $2$. There are many expression such as 'units of digit of $1872_{(9)}$ is 2', 'unit digit of $1872_{(9)}$ is 2' so on. What is the correct expression?

Moreover, consider $54_{(7)}$ and $32_{(7)}$. How can I refer to $4$ and $2$? In other words, what is the exact grammar referring to several unit digits?

Thanks.

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For $1872_{(9)}$, what is the correct expression when I refer 2 in number theory sense?

(1) the units of digit of $1872_{(9)}$ is 2

(2) the unit of digit of $1872_{(9)}$ is 2

(3) the unit digit of $1872_{(9)}$ is 2

(4) the units digit of $1872_{(9)}$ is 2

Answer 1

Taken from computer science, usually the $2$ in $432$ is referred to as the Least Significant digit, or LSd. and the $4$ would be the Most Significant digit, or MSd.

In any base, the right-most digit is the one with the least weight, thus is the least significant.

This also comes from the fact that a number in base $b$, can be written as, for $8762_b$ for instance $$8b^3+7b^2+6b^1+2b^0$$

the exponent of $b$ gives the order of the digits, then you can say digit $0$ is $2$, digit $1$ is $6$ etc...

Answer 2

Unsure if there is a more formal answer. I am satisfied to use a description that is unambiguous.

Given the number $1872_{(9)},$ I would describe the $2$ as either
the "one's digit" or
the "rightmost digit".