spc

type Chart struct {
	KPI    string  `json:"kpi"`
	Points []Point `json:"points"`
	// Centre is the mean; Lower and Upper the natural process limits,
	// the centre less and plus 2.66 average moving ranges.
	Centre float64 `json:"centre"`
	Lower  float64 `json:"lower"`
	Upper  float64 `json:"upper"`
	// Sigma is the process's spread estimated from the moving ranges.
	Sigma float64 `json:"sigma"`
	// Stable is no reading signalling; Enough is twenty readings or more,
	// the fewest the limits are usually trusted from.
	Stable bool `json:"stable"`
	Enough bool `json:"enough"`
	// SpecLower and SpecUpper are the KPI's specification limits, when it
	// has them; Cp and Cpk its capability against them, and SigmaLevel
	// the short-term sigma level, three times Cpk.
	SpecLower  *float64 `json:"specLower,omitempty"`
	SpecUpper  *float64 `json:"specUpper,omitempty"`
	Cp         *float64 `json:"cp,omitempty"`
	Cpk        *float64 `json:"cpk,omitempty"`
	SigmaLevel *float64 `json:"sigmaLevel,omitempty"`
	// Note says what the chart cannot yet tell.
	Note string `json:"note,omitempty"`
}

type Point struct {
	Period string  `json:"period"`
	Value  float64 `json:"value"`
	// Signals are the rules it breaks: beyond (a limit), run (the eighth
	// in a row on one side of the centre), trend (the sixth rising or
	// falling in a row).
	Signals     []string `json:"signals,omitempty"`
	Provisional bool     `json:"provisional,omitempty"`
}