"relatively steadily" is correct and can be used in written English.
You can use it to describe a gradual, but consistent increase or decrease in something over a period of time. For example, "Over the past three months, the company's profits have grown relatively steadily."
Birth rates for the same period declined relatively steadily by about one-fifth, to about three-fifths of the world average.
The rate has been falling relatively steadily since the early 1990s, and is now just over half the level it was in 1991.
During the past few decades, dividend yields have fallen relatively steadily in most economies, to the low single digits.
FMO extractable Fe decreases relatively steadily from ~1000 μg/g dry sediment at the top of the core to ~10 μg/g dry sediment at the bottom of the core.
The concentration dropped relatively steadily from that point, reaching a concentration of 0.008±0.002 μ 24 h post-injection.
Firstly, the three major cell wall components, cellulose, GAX and lignin, increased relatively steadily without any abrupt changes between the elongation, transition and maturation zones of the elongating internode.
4. The number of abortion providers has declined steadily since the mid-1970s, although it looks to have held relatively steady in the late 2000s.
Among the Palestinian minority in Israel, residential placement of people with intellectual disabilities [ID] is relatively new and steadily increasing, but poorly studied.
Any downturn in Firefox's growth can likely be chalked up to the growth being seen by Safari and Chrome, both of which still represent relatively small but steadily growing user bases.
Though his central convictions remained relatively stable, he steadily revised the details of his formulations in light of criticism from others and as a result of his own reconsideration.
Unemployment has fallen steadily and relatively consistently during both the Obama years and now President Trump's tenure, down to 3.9percentt in April.
