Working out the amount to inject is simple maths. If you use 2 x 1ml syringes of saline solution then 1 mg is 5 units on the syringe or half of the distance to the 10 marked on the side.
Apologies it may be simple maths but I got that wrong. If you have 2 x 1mL insulin syringes worth of liquid then 1 mg is 20 units on one of those syringes. (There are 200 units worth of liquid reconstituting 10mg so 1 mg is 1 tenth of 200 or 20 units on a syringe) The 5 units I referred to is actually 0.25 mg which is a good place to start to avoid the nausea side effect.