tokens: The NANOGrav Project receives support from NSF Physics Frontiers Center award number 1430284. Pulsar research at UBC is supported by an NSERC Discovery Grant and by the Canadian Institute for Advanced Research. The Arecibo Observatory is operated by SRI International under a cooperative agreement with the NSF (AST-1100968) and in alliance with Ana G. Méndez-Universidad Metropolitana and the Universities Space Research Association. The National Radio Astronomy Observatory and the Green Bank Observatory are facilities of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. W.W.Z. is supported by the CAS Pioneer Hundred Talents Program and the Strategic Priority Research Program of the Chinese Academy of Sciences, grant No. XDB23000000. Author Contributions. M.T.L. developed the mathematical framework for this work, created the modified set of profiles and short-term residuals, performed the analysis, and prepared the majority of the manuscript. M.A.M. assisted with the preparation of the manuscript. All authors performed observations and/or helped produce the initial pulse-profile data set. Additional specific contributions will be described in the future NANOGrav 12.5 yr data set paper. Software: PSRCHIVE (Hotan et al. 2004 ; van Straten et al. 2012 ), nanopipe (Demorest 2018 ), PyPulse (Lam 2017 ).
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