In order to make the formulas less cumbersome let

tₙ₁ - t₁ = v,
n₁ - 1
tʹₙ₁ - tʹ₁ = vʹ,
n₂ - 1
t₁ + t₂ + t₃ ... tₙ₁ = t,
n₁
and  tʹ₁ + tʹ₂ + tʹ₃ ... tʹₙ₂ = tʹ.
n₂

The correction to be made to the difference between Θₙ - Θ₁ for the influence of the outside temperature is determined by the formula of Regnault-Pfaundler, which is as follows:

∑ Δt = v - vʹ ( ⁿ⁻¹∑ Θr + Θₙ + Θ₁ - nt ) - (n - 1)v,
tʹ - t ₁ 2
n-1
in which ∑ Θr
1

is calculated from the observation of the thermometer Θ₁, Θ₂ etc., made immediately after the combustion. It is equal to the sum of observations Θ₁, Θ₂ etc., increased by an arbitrary factor equivalent to (Θ₂ - Θ₁)/9, which is made necessary by reason of the irregularity of the temperature increase during the first minute after combustion, the mean temperature during that minute being somewhat higher than the mean of the temperatures at the commencement and end of that time.

The quantity of heat formed by the combustion of the iron wire used for igniting the sample is to be deducted from the total heat produced. This correction may be determined once for all, the weight of the iron wire used being noted and that of any unburned portion being ascertained after the combustion.