I want a function to display x as a round of upto 3 decimal place as
12.457

Similarly truncate x at 3 decimal place as 12.456
irb(main):001:0> x=12.45678
=> 12.45678
irb(main):002:0> s = “%.3f” % x
=> “12.457”
irb(main):003:0> y = (x1000).round / 1000
=> 12
irb(main):004:0> y = (x1000).round / 1000.0
=> 12.457
irb(main):007:0> class Numeric
irb(main):008:1> def round_to( decimals=0 )
irb(main):010:2> factor = 10.0**decimals
irb(main):011:2> (self*factor).round / factor
irb(main):012:2> end
irb(main):013:1> end
=> nil
irb(main):014:0> y = x.round_to(3)
=> 12.457
irb(main):015:0> y = x.round_to(1)
=> 12.5
irb(main):016:0> y = x.round_to(-1)
=> 10.0

Note that ‘rounding’ the number is subject to floating point precision
errors. Subsequent printing of a number rounded to 3 decimal places
like the above may display as something like 12.4569999999999999999