     v_start = atof(arg);
     if (v_start < V_MIN || v_start > V_MAX)
     {
-      Serial.print("### Error: VSWEEP_START must have (");
+      Serial.print(F("### Error: VSWEEP_START must have ("));
       Serial.print(V_MIN,3);
-      Serial.print(" <= v_start <= ");
+      Serial.print(F(" <= v_start <= "));
       Serial.print(V_MAX,3);
-      Serial.print("), got:");
+      Serial.print(F("), got:"));
       Serial.print(v_start,3);
-      Serial.print(" ###\n");
+      Serial.print(F(" ###\n"));
       return;
     }
     _sweep_v_start = v_start;
   }
   else
   {
-    Serial.println("### Error: VSWEEP_START - requires 1 argument (float v_start) ###");
+    Serial.println(F("### Error: VSWEEP_START - requires 1 argument (float v_start) ###"));
   }
 }
 

    control_voltage = atof(arg);
    if (control_voltage < V_MIN || control_voltage > V_MAX)
    {
      Serial.print("### Error: VCTRL must have (");
      Serial.print(V_MIN,3);
      Serial.print(" <= control_voltage <= ");
      Serial.print(V_MAX,3);
      Serial.print(") ###\n");
      return;
    }
    control_DAC.setVoltageOutput(control_voltage + V_VGND); //shift to center-rail
  }
  else
  {
    Serial.println("### Error: VCTRL - requires 1 argument (float control_voltage) ###");
  }
}


  if (arg != NULL)
  {
    samp_rate = atof(arg);
    if (samp_rate >= SAMPRATE_MIN && samp_rate <= SAMPRATE_MAX)
    {
      _sweep_samp_rate = samp_rate;
      return;
    }
    else
    {
      Serial.print(F("### Error: VSWEEP.SAMPLE must have ("));
      Serial.print(SAMPRATE_MIN,3);
      Serial.print(F(" <= samp_rate <= "));
      Serial.print(SAMPRATE_MAX,3);
      Serial.print(F(") ###\n"));
      Serial.print(samp_rate);
      return;
    }
    
  }
  else
  {
    Serial.println(F("### Error: VSWEEP.SAMPLE - requires 1 argument (float samp_rate) ###"));
  }
}

