As has been mentioned, any two point protractor can be used to set up an SME, or any other arm for that matter, irrespective of whether the arm base slides, the mounting board pivots, or there are slots in the headshell.
The SME approach which is based on a nominal effective length design predates all current production arms and has many advantages, and is neither naive nor ill considered. As has been mentioned not all cartridges are the same, and the SME design principle was based on that fact.
Arc protractors are a relatively recent innovation, and are dependent on accurate effective length measurement, so as as to enable the correct arc to be created, otherwise the are inaccurate. They also require accurate mounting of the arm to suit the effective length. The SME approach does not require the pivot to spindle distance to be fixed, therefore the arm mounting is not critical. it is adjusted to suit the cartridge. Understanding this is important and there is much misinformation about SME arms because of a misunderstanding of the basis of tonearm design, often on the part of those who should know better.
There is a description of SME geometry here
as well as other aspects of design such as the importance of spindle sizes, and protractors such as the SME and the Dennesen Sountractor.
.
The SME approach which is based on a nominal effective length design predates all current production arms and has many advantages, and is neither naive nor ill considered. As has been mentioned not all cartridges are the same, and the SME design principle was based on that fact.
Arc protractors are a relatively recent innovation, and are dependent on accurate effective length measurement, so as as to enable the correct arc to be created, otherwise the are inaccurate. They also require accurate mounting of the arm to suit the effective length. The SME approach does not require the pivot to spindle distance to be fixed, therefore the arm mounting is not critical. it is adjusted to suit the cartridge. Understanding this is important and there is much misinformation about SME arms because of a misunderstanding of the basis of tonearm design, often on the part of those who should know better.
There is a description of SME geometry here
as well as other aspects of design such as the importance of spindle sizes, and protractors such as the SME and the Dennesen Sountractor.
.