The standard seems fairly unambiguous on this point, If your circuit is directly connected to mains with its accompanying risk of large overvoltages you may interpolate the creepage but not the clearance as long as the creepage is not less than the clearance. Presumably these hand held multimeters are battery powered and that the question of clearance interpolation only occurs as a result of wanting to test mains voltages of this rating. The option is open to you to specify a lower rating for work directly on mains voltages subject to transients than on well regulated supplies. If you specify polution degree 2, as is probably required for portable equipment that is likely to be used outdoors or taken suddenly from a hot to a cold place, then for most materials the creepage distance is substantially greater than the clearance and thus interpolation of the creepage distance down to the clearance distance is permissable. Nick Rouse
