how to typeset temporary tempo?

[Jinsong Zhao]

Hi there,

I am new to LilyPond. I try to typeset a music sheet. The following is a 
snippet. I don't satisfy the code in \markup, especially the size of the 
number.

\version "2.18.2"

\relative c'' {
  \clef "treble"
  \key ees \major
  \tempo 4 = 90

  f8 g f d ees2 ~ |%m75
  ees4 ees'2.\fermata ^\markup {\null \translate #'(2 . 0)  \magnify 
#0.5 \note #"4" #1 = "82"} |%m76
  bes4. aes8 g4 d'4 |%m77
  ees1 ~ |%m78
  ees1^\markup {\null \translate #'(2 . 0) \bold "rit." \magnify #0.5 
\note #"4" #1 = "75" } |%m79
  ees,,1 ~ |%m80
  ees1 \bar "|." %m81
}

Any suggestion or comments will be really appreciated. Thanks in advance.

Best regards,
Jinsong