Understand the relationship
The reasoning behind the result
Two observations establish an interval-average speed
vinterval = (x₂ − x₁)/(t₂ − t₁)
x₁ and x₂ are positions of the same marker measured from one origin; t₁ and t₂ are elapsed run times at those observations. The difference in positions divided by the positive time interval gives average forward speed in the selected distance/time units.
This average does not prove that speed was constant within the interval or will stay constant afterward. Equal positions produce zero observed speed. A reversed position is rejected because this workflow models forward progress; check the marker, origin and time ordering rather than silently taking an absolute value.
Remaining travel starts at the latest observation
Δx = xtarget − xcurrent; Δt = Δx/v; tarrival = tcurrent + Δt
For a target ahead of the current marker and positive speed, remaining distance divided by speed gives additional time. Elapsed arrival time includes time already spent. A speed inferred from a recent interval is not applied retrospectively to the full run.
If the target has already been reached or passed, remaining time is zero and any overrun is shown. This does not reconstruct the earlier crossing time. If speed is zero and the target is ahead, the model has no finite arrival time; zero is not substituted for that missing answer.
A future position follows the same stated speed assumption
xfuture = xcurrent + vΔt
Δt is an additional duration after the current observation. Multiplying speed by that duration gives additional distance, which is added to the recorded current position. The corresponding elapsed time is tcurrent + Δt.
Positions, speed and times use a consistent chosen unit system. To change millimetres to centimetres, divide both positions and speed by ten. To change minutes to seconds, multiply times by 60 and divide speed per minute by 60. The physical projection then remains the same.
A marker projection is not a separation protocol
Electrophoretic motion depends on the molecule, matrix, field, buffer and changing conditions. Voltage alone or a fragment's length cannot supply a universal speed. A measured interval can support a conditional short-range projection, with the continuing-speed assumption left explicit.
A tracking dye may move differently from the DNA or protein of interest. This tool does not prescribe a stop position, estimate band resolution, infer migration from a ladder's nominal sizes, control equipment or guarantee that a sample remains on the gel.
Follow the numbers
Use the latest measured interval without rewriting the past
- A marker is at 10 mm after 10 minutes and 22 mm after 20 minutes. Its interval-average speed is (22 − 10)/(20 − 10) = 1.2 mm/min.
- The entered target is 40 mm, leaving 40 − 22 = 18 mm from the latest observation.
- If speed remains 1.2 mm/min, additional time is 18/1.2 = 15 minutes and elapsed arrival time is 20 + 15 = 35 minutes.
- Dividing the full 40 mm by 1.2 would incorrectly apply the recent speed to the entire run. The current measured position anchors the projection instead.
The answer is a conditional projection from a recorded observation, not a universal run duration.
Quick guide
How to use this calculator
- Name the exact marker being tracked and use one position origin throughout. Keep a dye front distinct from the sample band of interest.
- Enter a known speed or two observations of that same marker. Observation time must increase; this tool models forward motion or no observed motion.
- Choose a future marker position or an additional duration. In measured-interval mode the latest observation is the starting point for the projection.
- Read the observed interval separately from the future constant-speed scenario. Re-measure if conditions change; an arrival calculation does not decide separation quality or when to stop a run.
Calculation method
Calculation and interpretation
Estimate a tracked marker's remaining travel under an explicit constant-speed assumption.
vinterval = (x₂ − x₁)/(t₂ − t₁); Δt = (xtarget − xcurrent)/v for a forward target and v > 0; xfuture = xcurrent + vΔt.
Worked example
Use the latest measured interval without rewriting the past
The answer is a conditional projection from a recorded observation, not a universal run duration.
vinterval = (x₂ − x₁)/(t₂ − t₁); Δt = (xtarget − xcurrent)/v for a forward target and v > 0; xfuture = xcurrent + vΔt.
Supported inputs
Precision and limits
Constant future speed is an assumption
Changes in voltage, current, temperature, buffer or matrix can change migration. Re-observe the named marker. No run settings, target position or separation-quality decision is supplied.
Position and timing records only
No image analysis, device connection or automatic stopping is performed. A stationary marker cannot produce a finite arrival time for a forward target. Numerical inputs support 10⁻⁹ through 10⁹ in their selected units; explicitly nonnegative positions and times also accept zero. These are calculation limits, not operating recommendations.
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