Plus42: incorrect behaviour in equation using temperature UOM

[Albert Chan]

(05-27-2024 04:21 PM)Thomas Okken Wrote:  The current implementation performs this consistent unit removal using UBASE and then UVAL. This works fine in most cases, but not with °C and °F, because of the offset introduced when UBASE converts those to K.

Perhaps we can add delta temperature unit? Δ°C = Δ°K, Δ°F = Δ°R, without offset

(9_Δ°C - 6_Δ°C) / LN( 9_Δ°C / 6_Δ°C )
= (9_Δ°K - 6_Δ°K) / LN( 9_Δ°K / 6_Δ°K )
= 3_Δ°K / LN(1.5)
= 3_Δ°C / LN(1.5)

We always convert to Kelvin, do math, then restore.
If 2 temperatures are plain Celsius, we get this instead.

(9_°C - 6_°C) / LN( 9_°C / 6_°C )
= ((9+273.15)_°K - (6+273.15)_°K) / LN( (9+273.15)_°K / (6+273.15)_°K )
= 3_Δ°K / LN(282.15/279.15)
= 3_Δ°C / LN(282.15/279.15)

Sum of temperatures make no sense. But with delta temp units, it does.

1_°C + 2_Δ°C = 3_°C      → 274.15_°K + 1_Δ°K = 275.15_°K