help with test of control & substantive testing

goldring

Hiya
I have trouble identifying which is which as above in some cases.

There are examples on e-learning:
for a sample of employess, re-perform the calculation of gross pay and deductions for PAYE,NI and pension contribution to ensure the calculation is correct. The model answer is test of control

then
reperform the depreciation of calculation for a sample of non-current asset,
and for a sample of disposal of non-current assets, ensure that profit/loss has been correctly calculated,
The model answer for both si substantive testing

I thought the first one is also substantive testing, as it tests the valuation as well?

Any one can explain it plainly?
tks