# boost/units - converting forces (lbf->N)

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## boost/units - converting forces (lbf->N)

 To see if I understand the library, I want to create metric and imperial systems without using Boost Units predefined systems*.  Conversions between lengths are going well.  Conversion between forces are going well until pounds-force to newtons; line 182 in the link.  What am I doing wrong when lbf will not convert to newtons?Here is my code: https://coliru.stacked-crooked.com/a/f5f80d39fbdf8013Any help is appreciated.* //imperial namespace boost {namespace units {namespace us {}}}//sinamespace boost {namespace units {namespace si {}}}_______________________________________________ Boost-users mailing list [hidden email] https://lists.boost.org/mailman/listinfo.cgi/boost-users
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## Re: boost/units - converting forces (lbf->N)

 On Sat, 1 Dec 2018 at 15:26, Matt Vinson via Boost-users <[hidden email]> wrote:To see if I understand the library, I want to create metric and imperial systems without using Boost Units predefined systems*.  Conversions between lengths are going well.  Conversion between forces are going well until pounds-force to newtons; line 182 in the link.  What am I doing wrong when lbf will not convert to newtons?Gravity is not your friend [and gets in the way of what you want to do], you're not doing anything wrong [C++-wise], but you're converting hamburgers to cheeseburgers [for free], they don't convert.From Wikipedia (https://en.wikipedia.org/wiki/Pound_(force)): The pound-force is equal to the gravitational force exerted on a mass of one avoirdupois pound on the surface of Earth. Since the 18th century, the unit has been used in low-precision measurements, for which small changes in Earth's gravity (which varies from place to place by up to half a percent) can safely be neglected.[4] The 20th century, however, brought the need for a more precise definition. A standardized value for acceleration due to gravity was therefore needed. degski-- “If something cannot go on forever, it will stop" - Herbert Stein _______________________________________________ Boost-users mailing list [hidden email] https://lists.boost.org/mailman/listinfo.cgi/boost-users
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## Re: boost/units - converting forces (lbf->N)

 In reply to this post by Boost - Users mailing list AMDG On 12/01/2018 06:25 AM, Matt Vinson via Boost-users wrote: > To see if I understand the library, I want to create metric and imperial systems without using Boost Units predefined systems*.  Conversions between lengths are going well.  Conversion between forces are going well until pounds-force to newtons; line 182 in the link.  What am I doing wrong when lbf will not convert to newtons? > There are a few problems. - BOOST_UNITS_DEFAULT_CONVERSION takes a unit (not a   base unit) as its second argument. - You are defining both a kilogram_base_unit and a kilo_gram_base_unit.   Either one will work, but you need to be consistent.  You're   defining the conversion in terms of kilo_gram_base_unit, but   metric::system uses kilogram_base_unit. - The definition of a composite conversion for force is not   needed and will be ignored. - metric and imperial have separate definitions of second_base_unit   with no conversion between them. - lbf is not the same as (lbm in s^-2) > Here is my code: >  https://coliru.stacked-crooked.com/a/f5f80d39fbdf8013> Any help is appreciated. > > * > //imperial > namespace boost {namespace units { > namespace us {}}}//sinamespace boost { > namespace units { > namespace si {}}} > In Christ, Steven Watanabe _______________________________________________ Boost-users mailing list [hidden email] https://lists.boost.org/mailman/listinfo.cgi/boost-users
 This has errors still (`lbf->N: 0.453592`, `N->lb: 0.183719`) and I am addressing them... On Saturday, December 1, 2018, 1:03:41 PM CST, Matt Vinson <[hidden email]> wrote: Thanks for response....Yes, yes, yes.  I get that.  I am having trouble understanding the library; not force.  (Same as last time)I guess I thought the library was magically accounting for gravity which is an error.Updated:https://coliru.stacked-crooked.com/a/d256de6c16bdb08fThank you, On Saturday, December 1, 2018, 9:10:38 AM CST, degski <[hidden email]> wrote: On Sat, 1 Dec 2018 at 15:26, Matt Vinson via Boost-users <[hidden email]> wrote:To see if I understand the library, I want to create metric and imperial systems without using Boost Units predefined systems*.  Conversions between lengths are going well.  Conversion between forces are going well until pounds-force to newtons; line 182 in the link.  What am I doing wrong when lbf will not convert to newtons?Gravity is not your friend [and gets in the way of what you want to do], you're not doing anything wrong [C++-wise], but you're converting hamburgers to cheeseburgers [for free], they don't convert.From Wikipedia (https://en.wikipedia.org/wiki/Pound_(force)): The pound-force is equal to the gravitational force exerted on a mass of one avoirdupois pound on the surface of Earth. Since the 18th century, the unit has been used in low-precision measurements, for which small changes in Earth's gravity (which varies from place to place by up to half a percent) can safely be neglected.[4] The 20th century, however, brought the need for a more precise definition. A standardized value for acceleration due to gravity was therefore needed. degski-- “If something cannot go on forever, it will stop" - Herbert Stein _______________________________________________ Boost-users mailing list [hidden email] https://lists.boost.org/mailman/listinfo.cgi/boost-users