We'd be happy to help you select an oscilloscope, and help determining that it can accurately measure your signal of interest. The best reference for this would be the oscilloscope documents that I have linked below.
• Evaluating Oscilloscopes: Learn About Key Features & Functions: https://www.tek.com/en/documents/primer/evaluating-oscilloscopes
• Oscilloscope Selection Guide: https://www.tek.com/en/documents/product-selector-guide/oscilloscope-selection-guide
• How to choose the best oscilloscope: https://www.tek.com/en/blog/which-oscilloscope-to-buy
However, a simple way to go quickly go about your request is to use your signals frequency or rise time and the ‘five times rule’. This rule states that the oscilloscope bandwidth and rise time specifications should be five times greater than that of your signal. This will help ensure better than 2% amplitude accuracy for your measurements.
Bandwidth and rise time are related via this equation: BW/[K/Rise time], where k is a value between 0.35 and 0.45. Oscilloscopes with bandwidth of <1 GHz typically have a 0.35 value, while oscilloscopes with a bandwidth of > 1 GHz usually have a value between 0.40 and 0.45.
In the example from your request, you state that you need a “a scope that has an uncertainty ± 0.125 µs or less”. I interpret this ‘± 0.125 µs’ value as a period specification. I would convert this value to frequency (Hz), P =1/f, 0.125us = 1/(f), f = 8MHz. This means that you need a scope with at least 8MHz bandwidth. Tektronix scope start at 50MHz, so any of our scopes should be capable of take this type of measurement.
From the general information I have reviewed, my current scope recommendation would be the 3 Series MDO or TBS1000C. The product pages for these scopes can be found below. Please feel free to review these and ask any questions you have.
• 3 Series MDO Mixed Domain Oscilloscope: https://www.tek.com/en/products/oscilloscopes/3-series-mdo
• TBS1000C Digital Storage Oscilloscope: https://www.tek.com/en/products/oscilloscopes/tbs1000
