Divising a DateTime by 1 or 10 yields different floating point precision

[K5Julien]

I have come to an inexplicable (at least for me at the moment) behavior in Julia

julia> using Dates
julia> Dates.value(Minute(60)) / 1 * 38.849
2330.9399999999996
julia> Dates.value(Dates.value(Minute(60)) * 38.849
2330.9399999999996
julia> Dates.value(Minute(60)) / 10 * 38.849
233.094
julia> Dates.value(Minute(60)) * 3.8849
233.094

Can you explain why the first two don’t yield the same precision as the two latest?

[screw_dog]

This isn’t about Dates, but rather that floating point arithmetic doesn’t work quite how one may expect. See:

3.8849 == 38.849/10 # false

This isn’t even about Julia, since Julia implements the industry standard IEEE 754 that most languages do.

Essentially, if you’re using floats you can’t usually use == as the order of operations can matter and slight differences can occur.

[nilshg]

That question is common enough that there’s a PSA:

PSA: floating-point arithmetic

Sometimes people are surprised by the results of floating-point calculations such as julia> 5/6 0.8333333333333334 # shouldn't the last digit be 3? julia> 2.6 - 0.7 - 1.9 2.220446049250313e-16 # shouldn't the answer be 0? These are not bugs in Julia. They’re consequences of the IEEE-standard 64-bit binary representation of floating-point numbers that is burned into computer hardware, which Julia and many other languages use by default. Brief explanation You can t…

[K5Julien]

Thanks for your replies
Just in case for future readers, what I actually wanted to ask has it answers here