ISO 3801 specifies different methods to determine mass per unit length and mass per unit area.
Method 5 specifies to use a square metal plate template. There are inconsistencies of the dimensions required, within the standard.
This is not available from James Heal.
Method 5 also recommends the use of a circular cutter.
James Heal offers the 100cm² circular cutter 230/100 (902-220).
Replacement blades are also readily available.
Circular cutters are quick and easy to use and offer increased levels of accuracy and precision.