Skip to content

EchoChrono

Overview

EchoChrono is a feature in the Precision Cut Archery mobile app that turns your phone into a chronograph for your compound bow.

Our goal with this is a valid alternative for those who don't have and can't afford a dedicated chronograph. To be totaly fair, a 'real' chronograph is still the best way to go if you can afford one, especially the top-tier radar units.

That said, when set up correctly, this is a very accurate alternative. See our Expected Accuracy section for more details.

EchoChrono is in Public Preview

Consider EchoChrono to be in testing. There may be bugs, issues, or improvements we can make.

If you know your arrow's actual speed, a session looks off, or we struggled to detect your shots, please send us a support bundle. There's a button at the bottom of each session. That's how we make this better!

How It Works

Your phone's microphone hears two sounds on every shot: the bow going off, and the arrow hitting the target. We're running signal processing and our ballistics engine to accurately determine your arrow's launch speed.

Because the whole measurement is built on a known distance, the distances from the target to your phone and phone to your bow have to be exact. Everything else is handled for you.

Expected Accuracy

With a tape-measured distance and positioning that matches the setup guide, expect readings within 1-3 fps of true speed.

Our current benchmarking against top-tier radar chronographs, from customer submissions:

  • Within 1 fps: 49% of sessions
  • Within 3 fps: 95% of sessions
  • Within 5 fps: 99% of sessions

Warning

Setup and distance are critical. A couple of inches of error is significant. Six inches of range error is about 5 fps of error in the reading, which is why we ask for a tape measure instead of a rangefinder.

Setup Guide

Location

  • Ideally outside, but inside can work.
  • Minimal wind and background noise.
  • A target that makes a distinct thwack makes the impact easier for us to find.

Phone

  • Exactly 20 yd (60 ft / 18.3 m) from the target face, at the height of your arrow at full draw.
  • Measure it with a tape measure. Rangefinders are not accurate enough for phone placement.
  • We recommend a 100' tape. We've seen quite a few measurement problems from chaining 25' tapes together.
  • A tripod is recommended to keep the phone in a consistent position.

You

  • Stand 6" (15 cm) to the side of the phone.
  • Position yourself so the nock leaves the string right on your measured 20 yd line, even with the phone.
  • At full draw, the end of your string stop should be on the 20 yd line.

Setup Diagram

Top-down diagram of the EchoChrono setup. The target is at the top and the measured 20 yard line runs across the bottom. The phone sits on that line facing the target, with the archer standing 6 inches to the side so the nock leaves the string on the same line, even with the phone

What You Enter

  • Arrow weight
  • Arrow length, measured from the nock groove to the tip, including the point and insert
  • Air temperature, used to correct for the speed of sound and air density

A rough temperature within a few degrees of actual is fine. Humidity and altitude are not needed.

Running a Session

  1. Enter your arrow weight, arrow length, and temperature, then tap Start New Session.
  2. Review the setup diagram and tap Continue.
  3. Work through the checklist, then tap Start Listening.
  4. Stay quiet for a second while we calibrate to the background noise, then shoot.
  5. Tap Stop Listening when you're finished.

Each shot gets an acoustics grade of Great, Fair, Weak, or Failed. This grades how clearly your phone heard the release and the impact, not how accurate the speed is. Failed shots are dropped and don't report a speed.

Tip

If you're getting a lot of Weak or Failed shots, the room or range is too echoey or too noisy. Move somewhere more open and quiet.