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\item \textbf{SKA1-SYS\_REQ-2962:} \textit{\bf SKA1\_Low Pulsar Timing resolution.} The SKA1\_Low when in pulsar timing mode shall resolve a pulsar's pulse profile with up to 2048 equal-width, contiguous phase bins of maximum resolution 1.6~us.  \end{itemize}  These two requirements should constrain both the acceptable channel widths provided to the SKA1 pulsar timing instruments and the polyphase filterbank design used to channelise the digitized baseband voltages. We envisage At level 2,  these requirements as being identical at level 2: will predominantly affect CSP\_Mid, CSP\_Low, and LFAA. There may also be minor implications for TM, DSH and SaDT. To provide design constraints for the CSP and LFAA we below define what we mean be ``effective time resolution'':  \indent  \textit{Definition: }\textbf{Effective Time Resolution for Pulsar Timing with SKA1}:  \begin{itemize}  \item \textbf{SKA-CSP.MID\_REQ-2961-00:} \textit{\bf CSP\_Mid Pulsar Timing resolution.} The CSP\_Mid when in pulsar timing mode shall resolve a pulsar's pulse profile with up to 2048 equal-width, contiguous phase bins of maximum resolution 200~ns.  \item \textbf{SKA-CSP.LOW\_REQ-2962-00:} \textit{\bf CSP\_Low Pulsar Timing resolution.} The CSP\_Low when in pulsar timing mode shall resolve a pulsar's pulse profile with up to 2048 equal-width, contiguous phase bins of maximum resolution 1.6~us.  \end{itemize}  At level 3 it is necessary to define ``effective time resolution'' to provide design constraints to the SKA1 beamformers   \begin{itemize}  \item \textbf{SKA-CSP.MID.CBF\_REQ-2961-00-00:} \textit{\bf CSP\_Mid Pulsar Timing resolution.} The CSP\_Mid when in pulsar timing mode shall resolve a pulsar's pulse profile with up to 2048 equal-width, contiguous phase bins of maximum resolution 200~ns.  \item \textbf{SKA-CSP.LOW.CBF\_REQ-2962-00-00:} \textit{\bf CSP\_Low Pulsar Timing resolution.} The CSP\_Low when in pulsar timing mode shall resolve a pulsar's pulse profile with up to 2048 equal-width, contiguous phase bins of maximum resolution 1.6~us.  \end{itemize}  While the above requirements would appear to satisfy the needs of the pulsar community, the practicality of these requirements is seriously undermined by the computational burden of performing coherent dedispersion at low frequencies on 10 MHz channels. This burden only becomes more difficult to manage as we move to larger dispersion measures (DMs). As such, the requirements suggested above need a modifier that allows them to change with DM. This modifier is provided by the physical limitations that interstellar scattering places on the minimum resolvable feature width in a pulse profile. This is discussed in detail below.