packageVersion("knitr")

## [1] '1.2'

options("digits")

## $digits
## [1] 4

a <- 100.101
a

## [1] 100.1

as.character(a)

## [1] "100.101"

options(digits = 4)
a

## [1] 100.1

options(digits = 10)
a

## [1] 100.101