A positive real number $z$ may be written as the sum of smaller integers ``digits'' $d_i < z$ multiplied by powers of a base $\beta$.
\begin{align}
z &= \displaystyle\sum_{i=-\infty}^{\infty} d_i \beta^{i}\label{fixedpointZ}
\end{align}
Where each digit $d_i < \beta$ the base. A set of $\beta$ unique symbols are used to represent values of $d_i$.
A seperate sign '-' can be used to represent negative reals using equation \eqref{fixedpointZ}.
To express a real number using equation \eqref{fixedpointZ} in practice we are limited to a finite number of terms between $i = -m$ and $i = n$. Fixed point representations are capable of representing a discrete set of numbers $0 \leq |z| \leq \beta^{n+1}-\beta^{-m}$ seperated by $\Delta z = \beta^{-m} \leq 1$. In the case $m = 0$, only integers can be represented.
Example integer representation in base 10 (decimal) and base 2 (binary):
\begin{align*}
5682_{10} &= 5\times10^3 + 6\times10^2 + 8\times10^1 + 2\times10^0 \\
1011000110010_2 &= 1\times2^{12} + 0\times2^{11} + \text{ ...} + 0\times2^0
\end{align*}
{\bf FIXME} Add Maths reference (Cantor's Diagonal argument) without going into all the Pure maths details
%, but could be represented by the combination of a numerator $7 = 111_2$ and denominator $3 = 11_2$. Lastly, some values such as $e \approx 2.718\text{...}$ can only be expressed exactly using a symbolical system --- in this case as the result of an infinite summation $e = \displaystyle\sum_n^{\infty} 1/n!$