This is the formula I currently have. Deleting the & still caused the whole formula to turn red and I'm not entirely sure why.
ActiveCell.FormulaR1C1 = "=IF(OR(R[17]C[-5]=0,R[18]C[-5]=0),""Invalid Input"",IF(AND(R[17]C[-5]<=4,R[18]C[-5]=0.105),'Laser Mark-Up'!R[-2]C[-6],IF(AND(R[17]C[-5]<=24,R[18]C[-5]=0.105),'Laser Mark-Up'!R[-2]C[-5],IF(AND(R[17]C[-5]<=99,R[18]C[-5]=0.105),'Laser Mark-Up'!R[-2]C[-4],IF(AND(R[17]C[-5]>=100,R[18]C[-5]=0.105),'Laser Mark-Up'!R[-2]C[-3]," _
& "IF(AND(R[17]C[-5]<=4,R[18]C[-5]=0.12),'Laser Mark-Up'!R[1]C[-6],IF(AND(R[17]C[-5]<=24,R[18]C[-5]=0.12),'Laser Mark-Up'!R[1]C[-5],IF(AND(R[17]C[-5]<=99,R[18]C[-5]=0.12),'Laser Mark-Up'!R[1]C[-4],IF(AND(R[17]C[-5]>=100,R[18]C[-5]=0.12),'Laser Mark-Up'!R[1]C[-3]," _
& "IF(AND(R[17]C[-5]<=4,R[18]C[-5]<=0.188),'Laser Mark-Up'!R[4]C[-6],IF(AND(R[17]C[-5]<=24,R[18]C[-5]<=0.188),'Laser Mark-Up'!R[4]C[-5],IF(AND(R[17]C[-5]<=99,R[18]C[-5]<=0.188),'Laser Mark-Up'!R[4]C[-4],IF(AND(R[17]C[-5]>=100,R[18]C[-5]<=0.188),'Laser Mark-Up'!R[4]C[-3]," _
& "IF(AND(R[17]C[-5]<=4,R[18]C[-5]<=0.313),'Laser Mark-Up'!R[7]C[-6],IF(AND(R[17]C[-5]<=24,R[18]C[-5]<=0.313),'Laser Mark-Up'!R[7]C[-5],IF(AND(R[17]C[-5]<=99,R[18]C[-5]<=0.313),'Laser Mark-Up''!R[7]C[-4],IF(AND(R[17]C[-5]>=100,R[18]C[-5]<=0.313),'Laser Mark-Up'!R[7]C[-3]," _
& "IF(AND(R[17]C[-5]<=4,R[18]C[-5]<=0.5),'Laser Mark-Up'!R[10]C[-6],IF(AND(R[17]C[-5]<=24,R[18]C[-5]<=0.5),'Laser Mark-Up'!R[10]C[-5],IF(AND(R[17]C[-5]<=99,R[18]C[-5]<=0.5),'Laser Mark-Up'!R[10]C[-4],IF(AND(R[17]C[-5]>=100,R[18]C[-5]<=0.5),'Laser Mark-Up'!R[10]C[-3]," _
& "IF(AND(R[17]C[-5]<=4,R[18]C[-5]=0.625),'Laser Mark-Up'!R[13]C[-6],IF(AND(R[17]C[-5]<=24,R[18]C[-5]=0.625),'Laser Mark-Up'!R[13]C[-5],IF(AND(R[17]C[-5]<=99,R[18]C[-5]=0.625),'Laser Mark-Up'!R[13]C[-4],IF(AND(R[17]C[-5]>=100,R[18]C[-5]=0.625),'Laser Mark-Up'!R[13]C[-3]," _
& "IF(AND(R[17]C[-5]<=4,R[18]C[-5]<=0.875),'Laser Mark-Up'!R[16]C[-6],IF(AND(R[17]C[-5]<=24,R[18]C[-5]<=0.875),'Laser Mark-Up'!R[16]C[-5],IF(AND(R[17]C[-5]<=99,R[18]C[-5]<=0.875),'Laser Mark-Up'!R[16]C[-4],IF(AND(R[17]C[-5]>=100,R[18]C[-5]<=0.875),'Laser Mark-Up'!R[16]C[-3]," _
& "IF(AND(R[17]C[-5]<=4,R[18]C[-5]>=1),'Laser Mark-Up'!R[19]C[-6],IF(AND(R[17]C[-5]<=24,R[18]C[-5]>=1),'Laser Mark-Up'!R[19]C[,IF(AND(R[17]C[-5]<=99,R[18]C[-5]>=1),'Laser Mark-Up'!R[19]C[-4],IF(AND(R[17]C[-5]>=100,R[18]C[-5]>=1),'Laser Mark-Up'!R[19]C[-3],""Invalid Input"")))))))))))))))))))))))))))))))))"
Edit: My formula is probably a lot messier than it needs to be, but I'm still learning. What I'm trying to do is have this formula look up a value on a table on the sheet "Laser Mark-Up" depending on the two variables that are put into designated cells.