Under bark, scanners and mill measurement: Sweden, Austria, Poland

Many mills now measure logs at the mill gate with scanners instead of calipers in the forest. This lesson shows how the Swedish, Austrian and Polish rules handle bark, taper and the place of measurement, and what a buyer should ask when a seller says "we use the mill measurement".

Sweden: two volumes and a bark function

The Biometria regulation (Sweden, Europe, in force 1 April 2025) defines two volumes:

• m3to, a cylinder with the log's length and the under-bark top diameter measured 10 cm from the top end.
• m3sub, the form-adjusted solid volume obtained by mid-point, top-butt, conversion-matrix or section measurement.

Section measurement uses sections of at most 50 cm that are summed, mainly with scanners approved by the authority (3D, shadow or X-ray). The regulation states that volume from top diameter and conversion factors may not be used as a basis for payment.

Under-bark diameter comes from a bark function Y = a + b x X, where Y is the double bark thickness in mm and X the top diameter over bark in mm. The under-bark diameter is X minus Y. Two published examples show how much the coefficients depend on species and area:

• Thin-bark pine in Norrbotten: y = 2.00 + 0.0153x.
• Spruce in "Area 1": y = 3.10 + 0.0496x.

Worked example. A log with top diameter over bark of 250 mm. For the Norrbotten pine function, Y = 2.00 + 0.0153 x 250 = 5.83 mm, so the under-bark diameter is 244.2 mm. For the spruce function, Y = 3.10 + 0.0496 x 250 = 15.5 mm, so the under-bark diameter is 234.5 mm (own calculation). The two functions differ by 9.7 mm in double bark thickness at the same top diameter. Do not carry the coefficients to another region or species.

The tracheid method of finding bark needs bark abrasion on at least 4% of the log surface; snow, ice, blue stain or long-term watering can stop it working. So even a calibrated scanner has conditions under which it does not work.

Austria: mill measurement and the sales letter

According to the Tyrol forest administration (Austria, Europe), round timber measurement follows Oe-NORM L1021 and the Holzhandelsusancen, and instruments for value-defining features must be calibrated. Two system types exist: MAWM (calibrated for mid-diameter, length, volume, taper and curvature) and RHMA (taper and curvature not calibrated).

Two phrases in the sales letter change who bears the cost:

• "Werksuebernahme": the seller accepts electronic mill measurement and may attend the takeover.
• "Waldabmass": the seller bears the takeover costs.

Staudenmaier (FVA, Germany, 2018) explains that mill measurement is contactless: length is the shortest distance between the ends, and diameter is simulated with a virtual caliper in two perpendicular planes after debarking. At the time harvester measurement could not be a sales measure in Germany for legal and technical reasons, and only one photo-optical pile system was calibratable for pile-front area (October 2018). These are 2018 statements; the current approval status was not verified.

Poland: technical conditions of the State Forests

Public Lasy Panstwowe documents (Poland, Europe, annex version mod2024) divide timber into large (W, minimum top diameter 14 cm without bark), medium (S, 5 cm) and small (M). Long logs (dluzyca) start at 6.1 m nominal length; logs (kloda) run 1.0 to 6.0 m. Mid-diameter is taken at half the length, and nominal length (used for volume) is distinguished from gross length; surpluses, reductions and end protection are excluded from volume.

The volume formula, bark deduction and rounding rules are not in these documents; PN-D-95000 and the older WZ rules were not found in an open source, so nothing is quoted from them.

What to ask about a mill measurement

1. Which regulation and edition applies, and is the system calibrated for the features that set the price?
2. Is volume under bark, and which bark function is used?
3. May the seller attend, and who pays for the takeover?
4. What happens when the scanner cannot read, for example with snow, ice or stain?
5. Are the raw data kept so that a disputed lot can be recomputed?

A mill that can answer these in writing has a defensible measurement. A mill that answers "it is the scanner" has not yet answered.

Key points

• Sweden separates m3to (a cylinder) from m3sub (form-adjusted volume); top-diameter-and-factor volumes are not allowed as a basis for payment.
• Bark functions are regional: at 250 mm top diameter over bark, the Norrbotten pine function gives 5.83 mm double bark, the Area 1 spruce function 15.5 mm (own calculation).
• In Austria, "Werksuebernahme" means mill measurement with the seller allowed to attend; "Waldabmass" puts takeover costs on the seller.
• Calibration status (MAWM or RHMA) tells you which features a system is approved to measure.
• Polish technical conditions use mid-diameter at half the length; their volume and rounding rules were not found in the open documents.