Creating a plane with 3 measurement features

If the plane is supposed to pass through the centres of the three spheres you can just use COLPTS to collect the centre points into a plane (see below)

COLPTS (NAM=PLANE, CSY=CSY(1), ELE=(SPH(1),SPH(2),SPH(3)), TYP=PLA, EVA=N)

However, if the spheres are offset then you will need to use the OFSPLANE command (see below)

OFSPLANE (NAM=OFFSET_PLANE, PTS=(SPH(1),SPH(2),SPH(3)), OFS=(10,20,30), MOD=NOE)

You enter the three offset values from the resulting plane to each corresponding sphere into the three boxes in the command dialogue (argument OFS).

If the plane is supposed to pass through the centres of the three spheres you can just use COLPTS to collect the centre points into a plane (see below)

COLPTS (NAM=PLANE, CSY=CSY(1), ELE=(SPH(1),SPH(2),SPH(3)), TYP=PLA, EVA=N)

However, if the spheres are offset then you will need to use the OFSPLANE command (see below)

OFSPLANE (NAM=OFFSET_PLANE, PTS=(SPH(1),SPH(2),SPH(3)), OFS=(10,20,30), MOD=NOE)

You enter the three offset values from the resulting plane to each corresponding sphere into the three boxes in the command dialogue (argument OFS).