The momentum resolution of the electromagnet can be defined as
, where P is the momentum of the parent beam and
is a combination of the intrinsic experimental momentum resolution and the momentum release due to photodissociation. The intrinsic experimental resolution (apparatus function) is inversely proportional to the width of the slits mounted on either side of the electromagnetic sector.
A measure of resolution was made by recording a momentum release, then recording a mass spectrum. To achieve sufficient resolution (i.e. when the momentum release width falls below the width of the intrinsic mass spectrum), narrow (24 and 50 m) slits were mounted on either side of the electromagnetic sector. This decreased the ion current arriving at the electron multiplier by an order of magnitude, hence decreasing the number of transitions for which a momentum release can be recorded.