[racket] what initial velocity to use when calculating velocity from acceleration (peripherally moby-related...)

Hi,

this is rather off topic, but as I can't find any useful information googling and know the nice and helpful people on this list, I try asking :-)

(Also, it's peripherally related as it's about calculating velocity from a smartphone's acceleration data using moby :-;)

To calculate velocity from acceleration I'd like to use Euler integration (at least this is what people normally seem to do), but I have no idea what to do about the initial velocity.
I cannot assume that the application is started exactly when a person starts to move, so the initial velocity will most certainly not be 0 but can be anything.

I've come across a post in some acoustics forum where someone mentioned using an integration constant, keeping averaging (what?) ... - but I didn't understand how.

It would be great if someone had a suggestion what I could do here...

Many thanks in any case,
Sigrid