Quotes Therefore, to change glucose from mg/
dL to mmol/L, one divides by 18.016
(usually rounded off to 18), and values
are multiplied by 18 to switch from
mmol/L to mg/dL. For example, 126
mg/dL is equivalent to 7.0 mmol/L, and
40 mg/dL is 2.2 mmol/L. 

 Quotes. Developing an HbA1c-Based Equation to Estimate Blood Glucose in Maintenance Hemodialysis Patients,2013
some equations showing a good correlation between HbA1c and average BG (AG) levels (the Diabetes Control and Complications Trial [DCCT] formula: AG = 35.6 × HbA1c − 77.3; 

        # pretty print from autoindent and ased editor
        # Convert HbA1c to Average Blood Glucose mg/dl V2
        # Console program example demo
        # written on Windows 10 on  TCL
        # working under TCL version 8.6
        # gold on TCL Club , 20aug2020
        # Each HbA1c reading usually from
        # limits of 4.0 to 11
        # has an equivalent average blood glucose
        # over a 3 month period.
        # formula from Diabetes Care, 2012.
        # Roughly 5 HbA1c converts to 100
        # mg/dl abbrev. for milligrams per deciliter
        # mmol/L abbrev. for milligrams per Liter
        package require Tk
        package require math::numtheory
        package require math::constants
        package require math::trig
        package require math
        namespace path {::tcl::mathop ::tcl::mathfunc math::numtheory math::trig math::constants }
        set tclprecision 17
        console show
        # following dresses up console output to easy eye
        console eval {.console config -bg palegreen}
        console eval {.console config -font {fixed 20 bold}}
        console eval {wm geometry . 40x20}
        set tclprecision 17
        # hbA1c_convert_to_average_blood_glucose mg/dl  HbA1c
        proc a1c hbA1c {  expr { 35.6*$hbA1c -77.3} }
        # convert mg/dl to mmol/L average blood glucose
        # some papers round off 18.016 to mgdl/18.
        proc mgdl_to_mmoll mgdl {  expr { $mgdl/18.0 } }
        # convert  mmol/L to mg/dl average blood glucose
        proc mmoll_to_mgdl mmoll {  expr { $mmoll*18.0 } }
        # proc precisionx used to round off floating point numbers
        proc precisionx {precision float}  {
            #  tcl:wiki:Floating-point formatting, <AM>
            # select numbers only, not used on every number.
            set x [ expr {round( 10 ** $precision * $float) / (10.0 ** $precision)} ]
            #  rounded or clipped to nearest 5ird significant figure
            set x [ format "%#.5g" $x ]
            return $x
        }
        proc table_format_out  n {
            set sum 0
            # initial hbA1c level
            set count 4.0
            puts "%| table|  | printed in|TCL format |% "
            puts "%| HbA1c units | mg/dl units |conv. mmol/L units  |comment, if any|% "
            # adapted proc from <RS>
            # printout in TCL WIKI format table
            for { set i 1 } { $i <= $n } { incr i } {
                set count [+ $count .1]
                set mgdl5 [ precisionx 3 [ a1c $count ]]
                set mmoll  [ precisionx 3 [mgdl_to_mmoll [ a1c $count ]]]
                puts "&| [ precisionx 3  $count ] | $mgdl5  | $mmoll | |&"
                incr sum $i
            }
            return $sum
        }
        proc comma_delimit_format n {
            set sum 0
            # initial hbA1c level
            set count 4.0
            puts "table, ,  printed in,  TCL format  "
            puts "HbA1c units , mg/dl units , conv. mmol/L units, comment, if any "
            # adapted proc from <RS>
            # printout in TCL  comma delimited format
            for { set i 1 } { $i <= $n } { incr i } {
                set count [+ $count .1]
                set mgdl5 [ precisionx 3 [ a1c $count ]]
                set mmoll  [ precisionx 3 [mgdl_to_mmoll [ a1c $count ]]]
                puts "[ precisionx 3  $count ] , $mgdl5, $mmoll ,  ,"
                incr sum $i
            }
            return $sum
        }
        table_format_out 90
        comma_delimit_format 90