Sentence:  A number of semiempirical estimates by various workers lead to the conclusion that the **f bond becomes symmetric when the **f bond length is about 2.4 to 2.5 <WSD>A</WSD> , but aside from the possible example of nickel dimethylglyoxime there have been no convincing reports of symmetric **f bonds . 
Meaning of the word marked with <WSD> tags:  a metric unit of length equal to one ten billionth of a meter (or 0.0001 micron); used to specify wavelengths of electromagnetic radiation