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The Nitty Gritty

For the technical rowers, curiosity about how the numbers appear on screen is natural. SplitRowr is built on a custom physics-based engine that prioritizes accuracy and smoothness, even when machine sensors are inconsistent.

Metric Calculation Formulas

500m Split (Pace)

The core metric of rowing. SplitRowr calculates this using the relationship between distance and time: Pace/500m = 500 / Velocity (m/s)

Power (Watts)

When raw watts aren’t provided by the machine, we derive them from the physical properties of the water or air resistance model: Watts = 2.8 * (Velocity in m/s)^3

Conversely, if a machine provides Watts but “garbage” pace data (an issue with some non-native rowers), we use the inverse to correct the split on-the-fly: Velocity = (Watts / 2.8)^(1/3)

Rower Calibration (The Factor)

Not all rowing machines are calibrated equally. A “2:00/500m” on a budget magnetic rower might feel like “1:45” effort on a Concept2.

SplitRowr uses a Calibration Factor to normalize your machine’s data to the Concept2 standard. Display Watts = Raw Watts * Factor

This ensures that your efforts in SplitRowr are comparable to the gold standard of indoor rowing, regardless of your hardware. You can select your Experience Level preset and run the calibration wizard in Settings > Rower Calibration.

How to Calibrate

  1. Prepare: Get on your rower and open the Settings > Calibrate menu.
  2. Row Steady: The wizard will ask you to row at a consistent, moderate effort for 30 seconds.
  3. Experience Check: The app will suggest a target pace based on your Experience Level (Beginner, Intermediate, Advanced) and your age/sex profile.
    • Example: A beginner might see a suggested target of 2:30/500m, while an advanced rower sees 1:55/500m.
  4. Auto-Correction: You confirm this is how the effort “felt,” or fine-tune it manually. SplitRowr then calculates the difference between your machine’s input and this target to generate a correction factor.

Weight Adjustment (Ghost Split)

“Ghost Splits” show what your pace would be if you were a standard 75kg rower. This allows for fair comparisons between rowers of different sizes: Factor = (Weight / 75.0)^(2/9) Ghost Split = Raw Split * Factor

Machine Compatibility (FTMS)

SplitRowr uses the Bluetooth Fitness Machine Service (FTMS) protocol. While this is a standard, implementation varies wildly between manufacturers.

Data Mapping

We parse the 0x2AD1 (Rowing Machine Data) characteristic. Since many machines only update distance in “chunks” (e.g., every 10 meters), SplitRowr uses high-frequency interpolation to ensure your distance counter moves smoothly every second.

Non-Standard Support

  • Keep-Alive Hack: Some rowers stop sending data if they think the session has paused. SplitRowr sends a hidden “Heartbeat” every second to keep the connection alive.
  • Elapsed Time Recovery: We identify and recover session timing data even from machines that don’t strictly follow the FTMS specification for time reporting.

Calories & Energy

SplitRowr offers two modes for calorie calculation, configurable in Settings:

This model, based on the Keytel (2005) study, uses your Heart Rate, Age, Weight, and Biological Sex to estimate energy expenditure. This accounts for your actual metabolic strain rather than just mechanical work, making it far more accurate for zone-based training.

2. Mechanical Model (Fallback)

When Heart Rate is unavailable or the setting is disabled, we use the industry-standard Concept2 Formula to estimate calories based on power output and weight: Calories/hr = (Watts * 4) + (1.714 * Weight in lbs)

[!NOTE] All biological metrics like Calories and Ghost Splits are significantly more accurate when you complete your User Profile in the app settings.