From 9a94d6da1bf16cf3826e390d63aa2469b4474449 Mon Sep 17 00:00:00 2001
From: rob tillaart <rob.tillaart@gmail.com>
Date: Mon, 27 Feb 2023 11:48:52 +0100
Subject: [PATCH] 0.2.0 SGP30 + add formula comment

---
 libraries/SGP30/SGP30.cpp | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/libraries/SGP30/SGP30.cpp b/libraries/SGP30/SGP30.cpp
index 96679d2bb..d0a718b40 100644
--- a/libraries/SGP30/SGP30.cpp
+++ b/libraries/SGP30/SGP30.cpp
@@ -269,6 +269,11 @@ float SGP30::getEthanol()
 //  CALIBRATION
 //
 
+//  slightly different formula
+//  https://carnotcycle.wordpress.com/2012/08/04/how-to-convert-relative-humidity-to-absolute-humidity/
+//  Absolute Humidity (grams/m3) = 6.112 × e^[(17.67 × T)/(T+243.5)] × rh × 2.1674
+//                                                 (273.15+T)
+
 //  T  in °C
 //  RH == RelativeHumidity
 float SGP30::setRelHumidity(float T, float RH)      //  Page 10
@@ -276,7 +281,7 @@ float SGP30::setRelHumidity(float T, float RH)      //  Page 10
   //  page 10 datasheet
   //  AH = AbsoluteHumidity
   //  uint16_t AH = 216.7 * RH/100 * 6.117 * exp((17.62 * T)/(243.12 + T)) / (273.15 + T);
-  float absoluteHumidity = (2.167 * 6.112) * RH ;
+  float absoluteHumidity = (2.167 * 6.112) * RH;
   absoluteHumidity *= exp((17.62 * T)/(243.12 + T));
   absoluteHumidity /=  (273.15 + T);