`Z` axis - depth
The `z` axis in maths is mainly thought of as depth.
In all situations however, the `z` axis is always 90° (perpendicular) to the `x` axis and `y` axis.
A deep sleep (depth) is lots of Z's (Z-Depth)
Example 1
Example 2
Example 3
![](/images/user/base/Maths/Logarithms/Reference%20Tables/reference-log-table-1.4df6ee6.jpg)
![](/images/user/base/Maths/Logarithms/Reference%20Tables/reference-log-table-2.d516bb3.jpg)
![](/images/user/base/Maths/Logarithms/Reference%20Tables/reference-anti-log-table-1.b0b0513.jpg)
![](/images/user/base/Maths/Logarithms/Reference%20Tables/reference-anti-log-table-2.f89189d.jpg)