Fixed some maths in manual for Kernel #3305

Job	Run time
codecheck / codecheck	43m 58s
conda / conda (ubuntu-20.04)	11m 23s
docker / docker (fedora39)	19m 59s
conda / conda (macos-13)	25m 28s
linux / linux (-doc-mpi-)	37m 41s
docker / docker (rocky8)	23m 53s
conda / conda (macos-14)	11m 44s
linux / linux (-mpi-)	52m 26s
mac / macports (macos-13)	14m 54s
linux / linux (-coverage-mpi-)	1h 3m 39s
mac / macports (+allmodules, macos-13)	24m 58s
linux / linux (-debug-)	30m 28s
mac / macsimple (macos-13)	20m 12s
linux / linux (-debug-mpi-)	50m 12s
mac / macsimple (macos-14)	5m 3s
linux / linux (-intel-)	46m 22s
linux / linux (-pycv-mpi-)	20m 38s
linux / linux (-nvhpc-mpi-)	57m 18s
	9h 20m 16s

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