Arms Ease of Movement (EMV)

Summary

Ease of Movement: the bar-to-bar move of the high-low midpoint divided by a box ratio of volume to range, averaged over a trailing window. It is the numeric form of Richard W. Arms, Jr.'s Equivolume box.

The box ratio is positive whenever the bar traded and has a range, so the sign follows the midpoint move. A large positive value means price rose easily, on light volume relative to its range; a large negative value means it fell easily. Values near zero mean volume was heavy for the distance travelled, or price hardly moved.

The output scales with the instrument's volume and with the volume divisor, so its level is comparable only within one instrument at one divisor. Traders mostly watch its sign and its zero crossings.

Formula

mid[i] = (high[i] + low[i]) / 2

box[i] = (volume[i] / D) / (high[i] - low[i])

raw[i] = (mid[i] - mid[i-1]) / box[i]

EMV[i] = ( sum_{k=i-N+1..i} raw[k] ) / N, N = optInTimePeriod, D = optInVolumeDivisor

A bar with no range or no volume has no box ratio and contributes 0. The next bar still measures its midpoint move from that bar.

Notes

The range is in price points. Achelis's text gives it in eighths of a point, the pre-decimal US quote unit; that reading is reached by multiplying the divisor by 8.
The divisor is a pure output scale: doubling it doubles every value. Pick one that suits the instrument's volume.
A period of 1 returns the unsmoothed one-bar values. Smoothing is a simple moving average; for an exponential one, apply EMA to this function's output at a period of 1.

Inputs

inHigh — High price of each bar
inLow — Low price of each bar
inVolume — Volume of each bar

Outputs

outReal — Ease of Movement, averaged over the window

Parameters

Parameter	Type	Default	Accepted values	Description
`optInTimePeriod`	integer	14	1–100000	Number of one-bar values in the simple moving average
`optInVolumeDivisor`	real	10000	≥ 1	Volume is divided by this before it forms the box ratio

Properties

Numerical Stability: Start-Independent


☐ Overlap Input
✅ Independent Y-Axis i
☐ Candlestick
☐ Can Output NaN or ±Inf
☐ Identity at Period 1

Implementation

TA-Lib Definition: emv.c · emv.yaml

Native	File
C	`ta_EMV.c`
Rust	`emv.rs`
Java	`Core_EMV.java`
C#	`Core_EMV.cs`

TA-Lib is also available for Python, R and more using a wrapper.

Aliases

Ease of Movement, EOM, Arms Ease of Movement

References

Richard W. Arms, Jr., Volume Cycles in the Stock Market: Market Timing Through Equivolume Charting, Dow Jones-Irwin, 1983.
Steven B. Achelis, Technical Analysis from A to Z, 2nd edition, McGraw-Hill, 2000, "Ease of Movement".
W. A. Thorp, Arms' Ease of Movement: Adding Volume to the Equation, AAII Journal, October 2001.
StockCharts ChartSchool, Ease of Movement (EMV).