The Rosary of the Blessed Virgin Mary is the most highly indulgenced sacramental
or prayer in the Church, outside of Holy Mass.

There are separate indulgences for every part of the Rosary:

For saying the Apostles' Creed
For saying the Our Father
For saying the Hail Mary
For saying the Glory Be to the Father
For praying an entire 5-decade Rosary with Creed, Pater, 3xAves, Glory Be, and then 5 decades while meditating on the 5 mysteries
For praying the entire 15-decade Rosary with all 15 mysteries
For praying the daily Rosary for a month, at least 5 decades a day
For holding standard, blessed, 5 decade or 15 decade Rosary beads while praying
For being in a group where someone is holding a blessed Rosary but you cannot because you are driving the car, or somehow unable to hold the beads yourself, so long as you join in the prayers
For praying the Rosary with a group of other people, in which case each individual gets the indulgences earned by the other individuals combined, such that 10 people each get 10 Rosary indulgences, and as a group, earn 100 indulgences together
For praying the Rosary in the presence of the Blessed Sacrament
For praying the Rosary in a church or oratory sacramentally dedicated for Catholic prayer
For praying the Rosary on certain feast days, such as the Feast of the Holy Rosary, October 7th
For adding prayers for the Holy Father, an Our Father, Hail Mary and Glory Be at the end of the Rosary

There may be more. These are cuмulative indulgences. That means, if you join a
group of 100 people on the Feast of the Holy Rosary, in a church, with the Blessed
Sacrament in the tabernacle, and each person holds their own blessed rosary
beads unless they are somehow unable, such as quadripelegic, and you pray 5
decades with the extra prayers for the Holy Father, then each person gets the
following:

100 Rosaries, before the Eucharist, on this Feast day, in a church, and prayers for
the Holy Father, holding blessed beads. That's 6 categories times 100 Rosaries, or
600 indulgences.

That would not be 100 or 600 plenary indulgences, because you can only get one
of those a day, except under rare conditions. But still, it's 600 partial indulgences
for each person, under the usual conditions.

Now, if you only pray one decade, there is only the indulgences for the individual
prayers, not for a Rosary. You have to pray in increments of 5 decades. You can
pray 10 decades, and that would be two Rosaries. Or you can pray 15 decades,
and that would be 3 Rosaries. When you do so, you don't have to repeat the
Credo, Pater, 3 Hail Mary's and Glory Be between each set of 5 decades in the
same day.

I went to a "Rosary" for a deceased friend and was alarmed to hear the
"permanent Deacon" announce that they would have a "decade," not a Rosary.
Then they led the Creed, Our Father, three Hail Mary's, Glory Be, and followed
that with the Resurrection decade (surprise, surprise). I made it a point to speak
with the "permanent Deacon" afterwards, to find that a "bereavement ministry"
couple had met with the family and asked questions, and checked boxes on their
form papers, including "Would you like to have a Rosary or a 'decade' for the
'viewing' ceremony?" The family answered that since many of the attendees would
be Protestants, they thought that a decade would be less offensive to them. I
asked the "permanent Deacon" if he knew anything about the indulgences for the
prayer of the Rosary. He said, "no." He's a "permanent Deacon" and he doesn't
know anything about indulgences. Right.

I asked him if the "bereavement ministry" form work has any mention of
indulgences for the Rosary, and he said, "no." I asked him if the "bereavement
ministry couple" ever explains to the family of the deceased anything about the
indulgences of the Rosary, and he said "no." Then I asked him, "Today, we had
about 150 people present, and if each one had prayed the 5 decade Rosary, how
many indulgences would that have been?" He replied, "I don't know." I informed
him that it could have been 22,500 Rosary indulgences for the repose of the soul
of the deceased, but instead, we only have one indulgence. So there are 22
thousand, four hundred and ninety nine indulgences lost today. He stared at me. I
asked him how there was one Rosary indulgence today, and he did not know that
either. That makes 5 for 5 for the "permanent Deacon." I have to wonder what
kind of "permanence" it refers to! I said that there was one Rosary indulgence
because I prayed one Rosary while they were goofing around with all the other
rigamarole that amounts to nothing but a performance for the entertainment
of the "assembly," I suppose, right in front of the deceased, who was a mother of
10 children, who always had a family Rosary at home or whenever they had a
road trip in the car (to keep the kids quiet!) but for her "veiwing" there was no
Rosary.

I went around and asked members of the assembly since everyone was chatting
in the church, like it's a stadium or theater or boxing arena, if they would have
been offended if we had prayed the 5-decade Rosary, and nobody said they
would have minded, in fact two thought it was odd that we had not done so.

You should always pray an entire decade without interruption. If you do get
interrupted, you should only stop at the end of a decade, lest you have to start
the decade over again when you resume. That's why an occupation with too many
interruptions is not conducive to praying the Rosary, unless you can manage to  
keep track of your prayers while doing something else.

Using the "ring" rosaries have not been useful for me, personally, because I do
not remember how many decades I have prayed. Sometimes I forget which
mystery I'm on, and then I don't know if it was one decade or two, or four or
three, or whatever. Therefore, I don't use the ring rosary beads. I found it
humorous when a friend of mine was promoting them by handing them out to
people after Mass, and when I went on a road trip with him, we prayed a Rosary
on three occasions, and each time, he forgot which mystery we were on! Too
much! I controlled my urge to tease him about it!