diff --git a/frappy_psi/razorbill.py b/frappy_psi/razorbill.py
index 7ee8c01..ad42db9 100644
--- a/frappy_psi/razorbill.py
+++ b/frappy_psi/razorbill.py
@@ -61,7 +61,7 @@ class Displacement(Readable):
         # calculate displacement from temperature and capacitance
         d0_T = self.d0_curve['a'] + self.d0_curve['b']*temp + self.d0_curve['c']*temp**2 + self.d0_curve['d']*temp**3 + self.d0_curve['e']*temp**4
 
-        disp = self.alpha290K / (cap - self.Cp) - self.d0 + d0_T
+        disp = self.alpha290K / (cap - self.Cp) - self.d0 - d0_T
 
         return disp
 
@@ -94,7 +94,7 @@ class Force(Readable):
         alpha = self.alpha290K * (0.91 + 5e-5*temp + 9e-7*temp**2)
         f0_T = self.f0_curve['a'] + self.f0_curve['b']*temp + self.f0_curve['c']*temp**2 + self.f0_curve['d']*temp**3 + self.f0_curve['e']*temp**4
         
-        force = alpha / (cap - self.Cp) - self.f0 + f0_T
+        force = alpha / (cap - self.Cp) - self.f0 - f0_T
 
         return force