TI-Nspire Engineering Economy Formulas and Shortcuts

TI-Nspire Engineering Economy Cheat Sheet

The Master Tools (F and G)

The Golden Rule: Look at the factor attached in the menu. The letter on the bottom of the fraction dictates what goes in that V slot.

Tool G: Present Worth (PW) Master Tool

Use to pull all money to Year 0 (today).

• Menu: V1 + V2*(P/A) + V3*(P/G) + V4*(P/F)
• V1 [No Factor]: Initial Investment (P). (Usually negative)
• V2 (P/A): Base Annual Income/Expense (A).
• V3 (P/G): Gradient Amount (G). (Amount A changes each year)
• V4 (P/F): Salvage Value / Future Value (F).

Tool F: Annual Worth (AW) Master Tool

Use to flatten all money into equal yearly amounts.

• Menu: V1 + V2*(A/P) + V3*(A/F) + V4*(A/G)
• V1 [No Factor]: Base Annual Income/Expense (A).
• V2 (A/P): Initial Investment (P). (Usually negative)
• V3 (A/F): Salvage Value / Future Value (F).
• V4 (A/G): Gradient Amount (G).

(Important: Press Enter after typing your final variable so the calculator refreshes the math!)

Problem Types and App Solutions

Capital Recovery (Equivalent Annual Cost)

• Look for: "Annual cost of ownership", Initial Cost + Terminal/Salvage Value.
• App Solution: Use Tool F (Annual Worth). Array setup: [0, -Cost, Salvage, 0].
• (Alternative: If there is no salvage value, use option 4: Equal Payments: Capital Recovery).

Arithmetic Gradients

• Look for: Cash flows change by a flat dollar amount (e.g., ±$500/year).
• App Solution: Use Tool G (PW) or Tool F (AW). Put starting amount in the A slot, and the change amount in the G slot. (Make G negative if profits are shrinking).

Geometric Gradients

• Look for: Cash flows grow by a percentage (e.g., +3% annually).
• App Solution: Do NOT use F or G. Use option 2: Geometric Gradient of Payments.

Project Evaluation (Accept or Reject?)

• Look for: "Is this project acceptable at a MARR of X%?"
• App Solution: Calculate Present Worth (Tool G) or Annual Worth (Tool F).
  • Positive (or 0): Accept the project.
  • Negative: Reject the project.

The Top 4 Traps

• The Net Income Trap: The problem lists revenues and expenses separately.
  • Fix: Subtract Expenses from Revenues to find your Net Cash Flow before using the calculator.
• The Negative Salvage Trap: The machine costs money to dispose of at the end of its life.
  • Fix: Enter the salvage value as a negative number in your array. It is a cost, not a credit.
• The Delayed Gradient Trap: The cash flow change doesn't start in Year 2 (e.g., Year 1: $3k, Year 2: $3k, Year 3: $2.8k).
  • Fix: You cannot use the Master Tools. Calculate it manually in pieces using individual P/A, P/G, and P/F tools.
• The Simple Payback Trap: A project asks for simple payback, but also provides a MARR %.
  • Fix: Simple Payback ignores interest. Calculate it (Cost / Annual Flow), but never use it to judge true profitability. Rely on the PW/AW analysis instead.