Frye FONIX FP40D - Manual (Page 48)

40 FONIX FP40 Portable Hearing Aid Analyzer
3. Align the sound opening of the aid with
the hole at the conical end of the coupler.
Look through the open end of the coupler
to be sure the sound opening of the aid is
clear of obstructions and correctly placed.
4. Seal the outside opening of any vent on
the aid with a small kernel of Fun-Tak.
5. Complete the acoustical sealing of the aid
to the coupler by using a pencil or finger.
You may want to double-check the aid
placement through the open end of the
coupler at this point.