The telemetry system does not rely on one number to decide whether a clock is running correctly. It observes the pendulum, the mechanical movement and the clock's position against true time, then uses those measurements together to decide whether correction is required.
← Return to Clock TelemetryThe telemetry system looks at the pendulum rate, then uses the centre-wheel hour-position event to establish where the mechanical clock actually is against true time. Comparing successive CWHP events shows whether that position error is reducing, increasing or remaining stable.
BPH means Beats Per Hour. The pendulum timing system measures the individual beats and calculates the rate at which the pendulum is oscillating.
For a clock whose target is 3600 BPH, exactly 3600 beats per hour represents the intended pendulum rate. Other clocks can have different target rates, such as 3150 BPH or 7200 BPH.
BPH Error is simply:
Time Rate Error converts that BPH difference into the equivalent number of seconds the clock would gain or lose per hour if that rate continued.
CWHP stands for Centre Wheel Hour Position. A sensor detects a magnet attached to a wheel that makes one revolution per hour. The magnet represents a known physical hour position of the movement, so the sensor creates a repeatable mechanical reference event once each hour.
This is the accurate RTC time at which the most recent centre-wheel hour-position event was detected.
The dashboard also shows the preceding valid CWHP event. Comparing the two event times makes the clock's movement from one hour to the next immediately visible.
CWHP gives us more than a rate measurement. Because the magnet represents a known physical hour position of the movement, the instant at which the sensor operates can be compared with the accurate time reference.
If the clock reaches its 14:00 mechanical position when true time is only 13:59:55, it reached the hour five seconds early.
If the clock reaches its 14:00 mechanical position when true time is 14:00:05, it reached the hour five seconds late.
This is the measurement that answers the very practical question: “How far ahead or behind true time is the clock right now?” The dashboard therefore presents a positive position as Seconds Fast, a negative position as Seconds Slow, and zero simply as On Time.
The four CWHP cards are arranged so that the reasoning can be followed directly from the two event times through to the correction decision.
Knowing that a clock is five seconds wrong is useful, but it is not enough to decide what to do. We also need to know whether that error is getting better or worse.
The clock is behind, but its error is naturally reducing. The correction engine can sensibly HOLD and allow the clock to continue moving towards zero.
The clock is behind and the error is increasing. The system now has evidence that corrective action may be required.
Position Change records how much the absolute clock position has moved since the previous valid CWHP event. Trend interprets that movement as towards zero, away from zero, or stable.
The correction engine does not simply react to one fast or slow reading. It considers the clock's absolute position and the direction in which that position is moving.
No change is presently required. This may be because the clock is already close to zero, because it is naturally correcting its position, or because further observation is preferable.
If a clock is behind and moving farther behind, the system may ADD WEIGHT to increase its rate.
If a clock is ahead and moving farther ahead, the system may REMOVE WEIGHT to reduce its rate.
A 3600 BPH clock contains a mathematical coincidence that can make two different measurements look as though they are the same thing.
Target 3600 BPH, measured 3598 BPH:
The two numbers happen to be numerically identical.
Target 3150 BPH, measured 3148 BPH:
Now the distinction becomes clear.
Therefore BPH Error is always expressed in BPH, while Time Rate Error is expressed in seconds per hour. They are related, but they are not the same measurement.
A quick reference to the principal measurements shown on the live telemetry dashboard.
| Parameter | What it tells us | Units / convention |
|---|---|---|
| Actual BPH | Measured pendulum beat rate. | Beats/hour |
| Target BPH | Expected pendulum beat rate for the clock being tested. | Beats/hour |
| BPH Error | Measured BPH minus Target BPH. | BPH; negative = below target |
| Time Rate Error | BPH Error converted into equivalent clock gain or loss per hour. | s/hour |
| Weight Position | Current correction-weight state. | OFF / ON / BLOCK |
| Current CWHP Event Time | Accurate RTC time recorded when the latest centre-wheel hour-position event occurred. | HH:MM:SS |
| Previous CWHP Event Time | Accurate RTC time of the preceding valid centre-wheel hour-position event. | HH:MM:SS |
| Position | Where the mechanical hour position occurred relative to true time. | Seconds Fast / Seconds Slow / On Time |
| Position Change | How much absolute clock position changed between valid CWHP events. | seconds/hour |
| Trend | Whether the position error is reducing, increasing or remaining stable. | Towards / Away / Stable |
| Estimate | Estimated time for the current position trend to reach zero. If there is no measurable one-hour convergence, the dashboard shows Not Applicable. | hours / Not Applicable |
| Correction | The correction engine's current decision. | HOLD / ADD / REMOVE |
| RTC Temperature | Temperature reported by the DS3231 RTC; this may differ slightly from room temperature. | °C |
| Clock Room Temperature | Ambient temperature measured near the clock. | °C |
| Humidity | Relative humidity around the clock. | % RH |
| Pressure | Atmospheric pressure measured by the environmental sensor. | hPa |
The pendulum provides the clock's fundamental rate. The centre-wheel sensor provides a repeatable mechanical hour-position event, and the accurate RTC time of that event tells us where the clock actually is relative to true time. Comparing successive positions then tells us whether the error is improving, worsening or remaining stable.
The correction engine combines those observations rather than trying to control the clock from a single number. That is why a clock can be fast or slow in absolute position while the correct decision is still to HOLD: what matters is not only where the clock is now, but whether that position is naturally moving towards or away from zero.