diff --git a/lib/node.ks b/lib/node.ks
index 55a0416..f9cf43b 100644
--- a/lib/node.ks
+++ b/lib/node.ks
@@ -39,10 +39,11 @@ function ExecNode {
   print "Node execution complete.".
 }
 
+// currently only works for testing against *current* stage.
 function WillStage {
   parameter dV.
   if not HASNODE { return false. }
-  return dV > NEXTNODE:DELTAV:MAG.
+  return dV > SHIP:StageDeltaV(SHIP:STAGENUM):VACUUM.
 }
 
 // Calculate the time required to burn a given dV.
@@ -54,19 +55,18 @@ function BurnTime {
   local lastStage is false.
   // We allow a small tolerance to deal with potential floating point errors.
   until totaldV <= 0.001 {
-    local F is stageThrust().
-    local Isp is stageISP().
+    local F is stageThrust(s).
+    local Isp is stageISP(s).
     local m is stageMass(s).
     // TODO: handle node execution in atmosphere?
     local dV is min(totaldV, SHIP:StageDeltaV(s):VACUUM).
     local t is calcBurnTime(dV, m, Isp, F).
-    print "DEBUG: " + dV + " m/s^2 in stage " + s + ", in " + t + " seconds.".
+
     set totaldV to totaldV - dV.
     set s to s - 1.
     set totalT to totalT + t.
   }
 
-  print "DEBUG: Total Burn Time: " + totalT + " s.".
   return totalT.
 }
 
@@ -74,8 +74,10 @@ function BurnTime {
 function calcBurnTime {
   parameter dV, m, Isp, F.
 
-  if F = 0 {
-    print "WARNING: Tried to calculate burn time with a thrust of 0. Returning 0. Your calculations are probably wrong.".
+  if F = 0 or Isp = 0 {
+    print "WARNING: Tried to calculate burn time with a denominator value of 0. Returning 0. Your calculations are probably wrong.".
+    print "F: " + F .
+    print "Isp: " + Isp.
     return 0.
   }
 
@@ -96,7 +98,7 @@ function stageISP {
   local eCount is 0.
   for e in en {
     if e:STAGE >= s and e:DECOUPLEDIN < s {
-      set ispSum to ispSum + e:ISP.
+      set ispSum to ispSum + e:VACUUMISP.
       set eCount to eCount + 1.
     }
   }
@@ -139,11 +141,14 @@ function stageMass {
   local ps is List().
   list PARTS in ps.
   for part in ps {
-    if part:DECOUPLEDIN <= s {
+    if part:DECOUPLEDIN >= s {
       set m to m - part:MASS.
-    } else if part:HasSuffix("AVAILABLETHRUST") and part:AVAILABLETHRUST > 0 {
-      // This is an engine and it is currently active. Subtract the fuel
-      // it will burn before the next stage.
+    }
+  }
+
+  list ENGINES in ps.
+  for part in ps {
+    if part:DECOUPLEDIN < s and part:AVAILABLETHRUST > 0 {
       set m to m - (part:MAXMASSFLOW * SHIP:StageDeltaV(SHIP:STAGENUM):DURATION).
     }
   }