Synchronous 4-bit, Mod16 counter with programmable reset - D-type flip flops 

This is a short video ahead of a more detailed lesson on how to derive and construct this circuit. The SPDT switches allow either Q or NOTQ for each of the four Q outputs. These feed an inverted 'And' gate (a NAND GATE) to provide an acitve-low reset on the desired count.
To count to 9 (1001) we must reset at 10 (1010).
We cannot use this logic unless we have a synchronous counter. A ripple counter will not perform as this circuit does.