diff --git a/pid.c b/pid.c
--- a/pid.c
+++ b/pid.c
@@ -11,8 +11,14 @@ void pid_init(pid_state_t* state)
 
 int16_t pid_update(therm_settings_t* set, therm_status_t* status, pid_state_t *state)
 {
+
+  // Convert temperature to fixed point number with 1/10th resolution
+  int8_t temp_frac = status->temp_frac > 9 ? status->temp_frac / 10 : status->temp_frac;
+  temp_frac = status->temp > 0 ? temp_frac : temp_frac * -1;
+  int32_t temp = (status->temp * 10) + temp_frac;
+
   // Calculate instantaneous error
-  int16_t error = status->setpoint - status->temp; // TODO: Use fixed point fraction
+  int16_t error = status->setpoint * 10 - temp; // TODO: Use fixed point fraction
 
   // Proportional component
   int32_t p_term = set->val.k_p * error;
@@ -26,7 +32,7 @@ int16_t pid_update(therm_settings_t* set
   // it cant help be cold despite its best efforts)
   // not necessary, but this makes windup guard values 
   // relative to the current iGain
-  int32_t windup_guard_res = set->val.windup_guard / set->val.k_i;
+  int32_t windup_guard_res = (set->val.windup_guard * 10) / set->val.k_i;
 
   // Calculate integral term with windup guard 
   if (state->i_state > windup_guard_res)
@@ -37,13 +43,12 @@ int16_t pid_update(therm_settings_t* set
   int32_t i_term = set->val.k_i * state->i_state;
 
   // Calculate differential term (slope since last iteration)
-  int32_t d_term = (set->val.k_d * (status->temp - state->last_pid_temp));
+  int32_t d_term = (set->val.k_d * (temp - state->last_pid_temp));
 
   // Save temperature for next iteration
-  state->last_pid_temp = status->temp;
-  state->last_pid_temp_frac = status->temp_frac;
+  state->last_pid_temp = temp;
 
-  int16_t result = p_term + i_term - d_term;
+  int16_t result = (p_term + i_term - d_term) / 10;
 
   // Put out tenths of percent, 0-1000. 
   if(result > 1000)