diff --git a/configtool/thermistortablefile.py b/configtool/thermistortablefile.py
index e03355a..ad57ba2 100644
--- a/configtool/thermistortablefile.py
+++ b/configtool/thermistortablefile.py
@@ -54,6 +54,7 @@ def generateTempTables(sensors, settings):
 
   ofp.output("#define NUMTABLES %d" % len(tl))
   ofp.output("#define NUMTEMPS %d" % N)
+  ofp.output("#define TEMPTABLE_FORMAT 1")
   ofp.output("");
 
   for i in range(len(tl)):
@@ -65,7 +66,7 @@ def generateTempTables(sensors, settings):
     ofp.close();
     return True
 
-  ofp.output("const uint16_t PROGMEM temptable[NUMTABLES][NUMTEMPS][2] = {")
+  ofp.output("const uint16_t PROGMEM temptable[NUMTABLES][NUMTEMPS][3] = {")
 
   tcount = 0
   for tn in tl:
@@ -102,6 +103,7 @@ def BetaTable(ofp, params, names, settings, finalTable):
 
   samples = optimizeTempTable(thrm, N, hiadc)
 
+  prev = samples[0]
   for i in samples:
     t = thrm.temp(i)
     if t is None:
@@ -113,14 +115,18 @@ def BetaTable(ofp, params, names, settings, finalTable):
 
     vTherm = i * vadc / 1024
     ptherm = vTherm * vTherm / r
+
     if i == max(samples):
       c = " "
     else:
       c = ","
-    ostr = ("    {%4s, %5s}%s // %4d C, %6.0f ohms, %0.3f V,"
-            " %0.2f mW") % (i, int(t * 4), c, int(t), int(round(r)),
-            vTherm, ptherm * 1000)
+
+    delta = (t - thrm.temp(prev)) / (prev - i) if i != prev else 0
+    ostr = ("    {%4s, %5s, %5s}%s // %4d C, %6.0f ohms, %0.3f V,"
+            " %0.2f mW, m = %6.3f") % (i, int(t * 4), int(delta * 4 * 256), c,
+            int(t), int(round(r)), vTherm, ptherm * 1000, delta)
     ofp.output(ostr)
+    prev = i
 
   if finalTable:
     ofp.output("  }")
@@ -145,6 +151,7 @@ def SteinhartHartTable(ofp, params, names, settings, finalTable):
 
   samples = optimizeTempTable(thrm, N, hiadc)
 
+  prev = samples[0]
   for i in samples:
     t = thrm.temp(i)
     if t is None:
@@ -157,8 +164,12 @@ def SteinhartHartTable(ofp, params, names, settings, finalTable):
       c = " "
     else:
       c = ","
-    ofp.output("    {%4d, %5d}%s // %4d C, %6d ohms" %
-               (i, int(t * 4), c, int(t), int(round(r))))
+
+    delta = (t - thrm.temp(prev)) / (prev - i) if i != prev else 0
+    ofp.output("    {%4d, %5d, %5d}%s // %4d C, %6d ohms, m = %6.3f" %
+               (i, int(t * 4), int(delta * 4 * 256), c, int(t), int(round(r))),
+               delta)
+    prev = i
 
   if finalTable:
     ofp.output("  }")
diff --git a/temp.c b/temp.c
index e0162cf..2095b21 100644
--- a/temp.c
+++ b/temp.c
@@ -196,28 +196,40 @@ static uint16_t temp_table_lookup(uint16_t temp, uint8_t sensor) {
         sersendf_P(PSTR("pin:%d Raw ADC:%d table entry: %d"),
                    temp_sensors[sensor].temp_pin, temp, j);
 
-      // Wikipedia's example linear interpolation formula.
-      // y = ((x - x₀)y₁ + (x₁-x)y₀) / (x₁ - x₀)
-      // y = temp
-      // x = ADC reading
-      // x₀= temptable[j-1][0]
-      // x₁= temptable[j][0]
-      // y₀= temptable[j-1][1]
-      // y₁= temptable[j][1]
-      temp = (
-      // ((x - x₀)y₁
-        ((uint32_t)temp - pgm_read_word(&(temptable[table_num][j-1][0]))) *
-                          pgm_read_word(&(temptable[table_num][j][1]))
-      //             +
-        +
-      //               (x₁-x)y₀)
-        (pgm_read_word(&(temptable[table_num][j][0])) - (uint32_t)temp) *
-          pgm_read_word(&(temptable[table_num][j - 1][1])))
-      //                        /
-        /
-      //                          (x₁ - x₀)
-        (pgm_read_word(&(temptable[table_num][j][0])) -
-         pgm_read_word(&(temptable[table_num][j - 1][0])));
+      #if (TEMPTABLE_FORMAT == 0)
+        // Wikipedia's example linear interpolation formula.
+        // y = ((x - x₀)y₁ + (x₁-x)y₀) / (x₁ - x₀)
+        // y = temp
+        // x = ADC reading
+        // x₀= temptable[j-1][0]
+        // x₁= temptable[j][0]
+        // y₀= temptable[j-1][1]
+        // y₁= temptable[j][1]
+        temp = (
+        // ((x - x₀)y₁
+          ((uint32_t)temp - pgm_read_word(&(temptable[table_num][j-1][0]))) *
+                            pgm_read_word(&(temptable[table_num][j][1]))
+        //             +
+          +
+        //               (x₁-x)y₀)
+          (pgm_read_word(&(temptable[table_num][j][0])) - (uint32_t)temp) *
+            pgm_read_word(&(temptable[table_num][j - 1][1])))
+        //                        /
+          /
+        //                          (x₁ - x₀)
+          (pgm_read_word(&(temptable[table_num][j][0])) -
+           pgm_read_word(&(temptable[table_num][j - 1][0])));
+        #elif (TEMPTABLE_FORMAT == 1)
+          // Linear interpolation using pre-computed slope.
+          // y = y₁ - (x - x₁) * d₁
+          #define X1 pgm_read_word(&(temptable[table_num][j][0]))
+          #define Y1 pgm_read_word(&(temptable[table_num][j][1]))
+          #define D1 pgm_read_word(&(temptable[table_num][j][2]))
+
+          temp = Y1 - ((((int32_t)temp - X1) * D1 + (1<<7)) >> 8);
+        #else
+          #error "temptable format unrecognized"
+        #endif
 
       if (DEBUG_PID && (debug_flags & DEBUG_PID))
         sersendf_P(PSTR(" temp:%d.%d"), temp / 4, (temp % 4) * 25);