HP 721A Operating And Servicing Manual page 21

Standard components have been used in this instrument,
whenever possible. Special components may be obtained
from your local Hewlett-Packard representative or from
the factory.
When ordering parts always, include:
1. {$& Stock Number.
2. Complete description of part including circuit
reference.
3. Model number and serial number of instrument,.
4. If part is not listed, give complete description,'
function and location of part.
Corrections to the Table of Replaceable Parts are listed
on an Instruction Manual Change sheet at the front of this
manual.
- RECOMMENDED SPARE PARTS LIST-
Column RS in the Table lists the recommended spare parts
quantities to maintain one instrument for one year of iso¬
lated service. Order complete spare parts kits from the
Factory Parts Sales Department. ALWAYS MENTION THE
MODEL AND SERIAL NUMBERS OF INSTRUMENTS INVOLVED.