It's impossible to definitively say which piece of scientific equipment is the "most widely used" because it depends on how you define "widely used."

Here are some contenders:

* Microscopes: Used in a vast range of disciplines, from biology and medicine to material science and engineering.

* Spectrometers: Used for analyzing the composition and properties of materials, crucial in chemistry, physics, and astronomy.

* Balances: Essential for measuring mass, used in various fields including chemistry, physics, and engineering.

* Thermometers: Used for measuring temperature in various fields, including healthcare, meteorology, and industry.

* Computers: Arguably the most essential tool in modern science, used for data analysis, modeling, simulations, and communication.

Ultimately, the "most widely used" piece of equipment depends on the context and criteria you consider. Each of these tools plays a critical role in scientific advancement and research.