diff --git a/lib/.eseries.c.kate-swp b/lib/.eseries.c.kate-swp
new file mode 100644
index 0000000..ca10a58
Binary files /dev/null and b/lib/.eseries.c.kate-swp differ
diff --git a/lib/eseries.c b/lib/eseries.c
index f1ccea5..bf858da 100644
--- a/lib/eseries.c
+++ b/lib/eseries.c
@@ -2,11 +2,11 @@
 
 #include"eseries.h"
 
-ESeriesMaxValue get_E_MAX(ESeries E_value) {
+ESeriesMaxValue get_E_MAX(ESeries E_series) {
 
     ESeriesMaxValue output;
 
-    switch(E_value) {
+    switch(E_series) {
         case E3:
             output = E3_MAX;
             break;
@@ -34,5 +34,8 @@ ESeriesMaxValue get_E_MAX(ESeries E_value) {
     }
 
     return output;
+}
+
+double round_to_E_series (double continuous_value, ESeries E_series) {
 
 }
diff --git a/lib/eseries.h b/lib/eseries.h
index 135780e..ce8af7c 100644
--- a/lib/eseries.h
+++ b/lib/eseries.h
@@ -21,6 +21,8 @@ double *E_values[7] = {E3_values, E6_values, E12_values, E24_values, E48_values,
 typedef enum {E3, E6, E12, E24, E48, E96, E192} ESeries;
 typedef enum {E_NIL=0, E3_MAX=3, E6_MAX=6, E12_MAX=12, E24_MAX=24, E48_MAX=48, E96_MAX=96, E192_MAX=192} ESeriesMaxValue;
 
-extern ESeriesMaxValue get_E_MAX(ESeries E_value);
+extern ESeriesMaxValue get_E_MAX(ESeries E_series);
+
+extern double round_to_E_series (double continuous_value, ESeries E_series);
 
 #endif /*ESERIES_H*/
diff --git a/lib/max_functions.c b/lib/max_functions.c
index 47fb3d4..24c364c 100644
--- a/lib/max_functions.c
+++ b/lib/max_functions.c
@@ -2,27 +2,93 @@
 
 #include"max_functions.h"
 
-void set_output_voltage(double setpoint_voltage, ESeries E_resistors) {
+int set_output_voltage(double setpoint_voltage, ESeries E_resistors) {
+
+    bool solution_found = false;
+    int decade_max = 6;
+    int decade_min = 1;
 
     double R_high_resistance = 0.0;
     double R_low_resistance = 0.0;
 
-    //start at 10k for low resistor and at 1R for high resistor
-    int R_high_decade = 0;
+    //start at 10k for low resistor and at minimum for high resistor
+    int R_high_decade = decade_min;
     int R_low_decade = 4;
+    double R_high_value = 1.00;
+    double R_low_value = 1.00;
 
     // voltage computed from resistor configuration used to compare new result to previous optimum
     double output_voltage = 0.0;
+    double output_voltage_w = 0.0;
 
     // set the max array index for given e series
-    ESeriesMaxValue max_value = get_E_MAX(E_resistors);
+    unsigned int e_max_values = get_E_MAX(E_resistors);
+    if (e_max_values == E_NIL) {
+        printf("max668_calc:max_functions:set_output_voltage: Unknown E series.\n");
+        return EXIT_FAILURE;
+    }
+
+    // working variables
+    int R_high_decade_w = R_high_decade;
+    int R_low_decade_w = R_low_decade;
+    double R_high_value_w = R_high_value;
+    double R_low_value_w = R_low_value;
 
     /*
      * start at minimum given Rlow from datasheet and select optimal Rhigh for given Rlow and Vout.
      * do this for all possible Rlows and choose the optimal combination
      * (minimize |setpoint_voltage - output_voltage|)
      */
-    for () {
+    for(int i_low = R_low_decade; i_low <= 6; i_low++) {
 
+        R_low_decade_w = i_low;
+
+        for (int j_low = 0; j_low < e_max_values; j_low++) {
+
+            // in the 6th decate only examine R_low = 1M, then stop
+            if ( i_low == 6 && j_low > 0 )
+                break;
+
+            // select new R_low
+            R_low_value_w = E_values[E_resistors][j_low];
+            R_low_resistance = R_low_value_w * exp(log(10)*R_low_decade_w);
+
+            // calculate corresponding R_high
+            R_high_resistance = R_low_resistance *((setpoint_voltage/1.25)-1);
+            R_high_decade_w = floor(log10(R_high_resistance));
+            R_high_value_w = round_to_E_series((R_high_resistance / exp(log(10)*R_high_decade_w)), E_resistors);
+
+            // calculate the acchieved outputvoltage for resistor combination from the given E series
+            output_voltage_w = 1.25 * ((R_high_resistance/R_low_resistance) + 1);
+
+            // if the calculated resistance is too small or too great, ignore it
+            if (R_high_decade_w > decade_max || R_high_decade_w < decade_min)
+                continue;
+
+            // if a new optimum is found -> save the values
+            if (fabs(output_voltage - setpoint_voltage) > fabs(output_voltage_w - setpoint_voltage)) {
+                R_high_decade = R_high_decade_w;
+                R_high_value = R_high_value_w;
+                R_low_decade = R_low_decade_w;
+                R_low_value = R_low_value_w;
+                output_voltage = output_voltage_w;
+                solution_found = true;
+            }
+        }
     }
+
+    // report the found optimal resistor combination in the given E series
+    if (solution_found) {
+        printf("Found optimal combination for R_high / R_low: \n");
+        printf("R_low: %5.2fE%i ohms\n",R_low_resistance,R_low_decade);
+        printf("R_high: %4.2fE%i ohms\n",R_high_resistance,R_high_decade);
+        printf("Achieved output_voltage:");
+        printf("V_out: %4.2f",output_voltage);
+    }
+    else {
+        printf("max668_calc:max_functions:set_output_voltage: Unable to find valid resistance combination within given range.\n");
+        return EXIT_FAILURE;
+    }
+
+    return EXIT_SUCCESS;
 }
diff --git a/lib/max_functions.h b/lib/max_functions.h
index 616bfc2..a578d8a 100644
--- a/lib/max_functions.h
+++ b/lib/max_functions.h
@@ -2,8 +2,13 @@
 #ifndef MAX_FUNCTIONS_H
 #define MAX_FUNCTIONS_H
 
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+#include <stdbool.h>
+
 #include "eseries.h"
 
-extern void set_output_voltage(double voltage, ESeries E_resistors);
+extern int set_output_voltage(double voltage, ESeries E_resistors);
 
 #endif /*MAX_FUNCTIONS_H*/
diff --git a/main.c b/main.c
index 210cab8..c377bc1 100644
--- a/main.c
+++ b/main.c
@@ -1,3 +1,4 @@
+/*main.c*/
 #include <stdio.h>
 #include <stdlib.h>