A subset $B$ of a group $G$ is called a difference basis of $G$ if each element $gin G$ can be written as the difference $g=ab^{-1}$ of some elements $a,bin B$. The smallest cardinality $|B|$ of a difference basis $Bsubset G$ is called the difference size of $G$ and is denoted by $Delta[G]$. The fraction $eth[G]:=Delta[G]/{sqrt{|G|}}$ is called the difference characteristic of $G$. We prove that for every $ninmathbb N$ the dihedral group $D_{2n}$ of order $2n$ has the difference characteristic $sqrt{2}leeth[D_{2n}]leqfrac{48}{sqrt{586}}approx1.983$. Moreover, if $nge 2cdot 10^{15}$, then $eth[D_{2n}]<frac{4}{sqrt{6}}approx1.633$. Also we calculate the difference sizes and characteristics of all dihedral groups of cardinality $le80$.
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