Formula for Value-Combination (FIXED, LEN) doesn't work with values with changed decimal places

I wrote a formula to combine a value and its standard deviation in one cell.

Cell A1: 2.945

Cell B1: 0.003

formula: =FIXED(A1;(LEN(B1)-2))&"("&(B1*(10^(LEN(B1)-2))&")")

Result: 2.945(3)

In my area of work this way of adding the standard deviation with paranthesis to the end is common.

The formula works fine for unchanged numbers. When i actively change the decimal places (like reduce it to 3 places), the formula recognizes the length of the starting number. The result is shown below:

A1: 0.237

[edit: Values in A1 are also reduced to lower decimal places: 0.237000961170212]

B1: 0.00244365421481958 --> 3 decimal places --> 0.002

Result:

0.23700096117021200(244365421481958)

desired result:

0.237(2)

This is a direct copy of my reddit post:
https://www.reddit.com/r/excel/comments/lms79r/formula_for_valuecombination_fixed_len_doesnt/?utm_source=share&utm_medium=web2x&context=3