For a small lab project I was asked to measure the propagation delay of a SN7400N NAND-Gate. In order to do this i connected one input pin to 5V and the other one to a clock running at 1 kHz. I connected an oscilloscope to the output and plotted it (top signal) together with the clock signal (bottom signal). As far as I know the delay is measured from 50% voltage to 50% voltage which would be about 1.5 squares, which is about 375 ns. This is far longer than the one in the specification (22ns).
Question: Where does this difference come from? Is it due to the input capacitance of the oscilloscope? Is it related to the frequency of the clock?