Displaying Results when they are very, very small

Maybe someone has asked this before. What about when tha result of a calculation is very small? I mean, if you work in molecular chemistry, some quantities are very small, I mean the power of ten are negative and big for these quantities. Computing an energy, MathCad 14 wrote U=0.J , but if I multiply the left side by 100000, the answer is 100000.U=8.7 e-15 J, but if the factor is 10000 (or lower), MathCad says 10000.U= 0.J again.

How can I prevent to happend this?

Thanks, I know MathCad is a great software.