The one that includes more than one type of unit is known as complex measurement.
$$2^\circ \ 23' \ 12''$$
$$2h \ 23\mbox{min} \ 12\mbox{s}$$
The simple measurement is the one that uses only one type of unit.
$$2,25$$ hours
$$135$$ minutes
If, for example, we want to convert $$2\mbox{h} \ 23\mbox{min} \ 12\mbox{s}$$ into seconds, it is necessary to use the conversion factors to find all three values in seconds, and finally add them up.
$$$2\mbox{h} \cdot \dfrac{60\mbox{min}}{1\mbox{h}}\cdot\dfrac{60\mbox{s}}{1\mbox{min}}=7.200\mbox{s}$$$
$$$23\mbox{min}\cdot\dfrac{60\mbox{s}}{1\mbox{min}}=1.380\mbox{s}$$$
$$$12\mbox{s}$$$
$$$7.200+1.380+12=8.592\mbox{s}$$$
Converting from simple measurement to complex measurement
Two cases will be analyzed:
1.- Converting from minor units in to higher units: $$7.523$$ seconds into seconds, minutes and hours.
In this case, it will be necessary to divide by $$60$$ twice.
$$\begin{eqnarray} &7523'' & |\underline{60} & & \\\\ & 23'' & 125' & |\underline{60} \\\\ & & 5' & 2^\circ \end{eqnarray}$$
$$7523''=2^\circ \ 5' \ 23''$$
2.- Converting to lower units: $$3,38$$ hours to seconds, minutes and hours.
In this case it will be necessary to multiply by $$60$$.
$$3,38\mbox{h} \left\{ \begin{array}{c} 3\mbox{h} \\ 0,38\cdot60=22,8\mbox{min} \end{array} \right. \rightarrow 22,8\mbox{min}$$
$$22,8\mbox{min} \left\{ \begin{array}{c} 22\mbox{min} \\ 0,8\cdot60=48\mbox{s} \end{array} \right.$$
Namely,
$$3,38\mbox{h} = 3h \ 22' \ 48''$$