This memo aims to address and update the following level 1 system requirements for pulsar timing with SKA1_Low and SKA1_Mid:
SKA1-SYS_REQ-2961: SKA1_Mid Pulsar Timing resolution. The SKA1_Mid Pulsar timing mode shall have a timing resolution of better than 100 ns.
SKA1-SYS_REQ-2962: SKA1_Low Pulsar Timing resolution. The SKA1_Low Pulsar timing mode shall have a timing resolution of better than 100 ns.
We will approach this in two ways: Firstly we will look at the maximum timing resolution that can be envisaged as being required for pulsar timing with SKA1 and secondly we will consider how multi-path scattering imposes further limits on timing resolution as a function of dispersion measure.