Aside from counting on fingers and toes, experts say the oldest computing tool is the abacus. That device—which used strings of beads or shells to represent place value—probably originated in Sumer (in the area that is now Iraq) in 2500 BC. It worked so well that the abacus is still used by merchants and teachers in some places.

Handheld calculators didn’t show up until the 1970s when microchips made it possible to produce tiny digital devices on the cheap. Now scientific calculators amp up basic models by enabling advanced functions and sophisticated display formats. Here’s what to look for when picking the right tool for the math job.

This option displays equations and symbols in textbook format for clarity. Texas Instruments

Math is complicated enough, so it’s crucial to pick a scientific calculator that’s easy to use and easy to read. Some models have advanced display options—sometimes called MathPrint or Natural Textbook—that show expressions, symbols and fractions in the same format as a textbook. That makes it easier to check your work.

Use the embedded scrolling feature to review previous work. Texas Instruments

Advanced math functions mean solving multiple steps. Look for a calculator that includes an entry line scrolling feature so you can flip through previous entries and look for patterns. That’s helpful in math class and even awesomer if you’re running science experiments.

This tool uses solar power and includes a backup battery for reliability. Casio

We like our scientific calculators like we like our coffee: strong and always available. Models that come with a hard case protect the instrument from damage when bouncing around in a backpack or sitting on a lab bench. Look for an option with solar power plus a backup battery to ensure the calculator is always ready when you need it.