Update README.md

README.md

@@ -10,7 +10,7 @@ First, I copied the firmware code for Arduino platform from that page, then I he
 2. Unnecessary Adafruit_NeoPixel.h and Adafruit_NeoPixel.cpp files have been removed.
 3. A software bug in maxim_heart_rate_and_oxygen_saturation() function in algorithm.cpp has been fixed: after applying 4-point moving average, the an_x[] still contained original last three points (an_x[97], an_x[98], an_x[99]). Subsequent code still referred to the full an_x[] array (0-99) instead of its averaged portion (0-96).
 4. In algorithm.h the "uint8_t uch_spo2_table[184]" has been replaced by "float uch_spo2_table[184]", where the original integers have been recalculated into floating point numbers with 6 decimal digits precision.
-5. A completely new algorithm of signal processing and resulting heart rate and SpO2 calculation has been designed and placed in new files algorithm_by_RF.h and algorithm_by_RF.cpp. The algorithm has been described and published in the following Instructable: ().
+5. A completely new algorithm of signal processing and resulting heart rate and SpO2 calculation has been designed and placed in new files algorithm_by_RF.h and algorithm_by_RF.cpp. The algorithm has been described and published in the following Instructable: https://www.instructables.com/id/Pulse-Oximeter-With-Much-Improved-Precision/.
 6. The RD117_ARDUINO.ino file has been rewritten from the ground up. Code for saving oximetry data to an SD card has been added, algorithm_by_RF has been made default, while Maxim's algorithm has been made optional. Integer variables were replaced by floating point variables, where applicable.
 
 The following two crucial constants are defined in algorithm_by_RF.h: